diff --git a/.github/workflows/build-pkg.yml b/.github/workflows/pkg-installer.yml
similarity index 69%
rename from .github/workflows/build-pkg.yml
rename to .github/workflows/pkg-installer.yml
index 5818320765..1862646b28 100644
--- a/.github/workflows/build-pkg.yml
+++ b/.github/workflows/pkg-installer.yml
@@ -1,28 +1,31 @@
-name: Build Homebrew installer pkg
+name: Installer Package
 on:
   push:
+    branches:
+      - '**'
+    tags-ignore:
+      - '**'
     paths:
-      - .github/workflows/build-pkg.yml
+      - .github/workflows/installer-package.yml
       - package/**/*
   release:
     types:
       - published
-
+env:
+  PKG_APPLE_DEVELOPER_TEAM_ID: ${{ secrets.PKG_APPLE_DEVELOPER_TEAM_ID }}
+  HOMEBREW_NO_ANALYTICS_THIS_RUN: 1
+  HOMEBREW_NO_ANALYTICS_MESSAGE_OUTPUT: 1
 jobs:
   build:
     if: github.repository_owner == 'Homebrew'
-    runs-on: macos-13
-    permissions:
-      # To write assets to GitHub release
-      contents: write
+    runs-on: macos-latest
+    outputs:
+      installer_path: "Homebrew-${{ steps.homebrew-version.outputs.version }}.pkg"
     env:
       TEMPORARY_CERTIFICATE_FILE: 'homebrew_developer_id_installer_certificate.p12'
       TEMPORARY_KEYCHAIN_FILE: 'homebrew_installer_signing.keychain-db'
-      # Set to the latest supported version of macOS
-      MIN_MACOS_VERSION: '12.0'
-      PKG_APPLE_DEVELOPER_TEAM_ID: ${{ secrets.PKG_APPLE_DEVELOPER_TEAM_ID }}
-      HOMEBREW_NO_ANALYTICS_THIS_RUN: 1
-      HOMEBREW_NO_ANALYTICS_MESSAGE_OUTPUT: 1
+      # Set to the oldest supported version of macOS
+      HOMEBREW_MACOS_OLDEST_SUPPORTED: '12.0'
     steps:
       - name: Remove existing API cache (to force update)
         run: rm -rvf ~/Library/Caches/Homebrew/api
@@ -58,7 +61,9 @@ jobs:
         run: security import "${RUNNER_TEMP}/${TEMPORARY_CERTIFICATE_FILE}"
                              -k "${RUNNER_TEMP}/${TEMPORARY_KEYCHAIN_FILE}"
                              -P "${PKG_APPLE_SIGNING_CERTIFICATE_PASSWORD}"
-                             -t cert -f pkcs12 -A
+                             -t cert
+                             -f pkcs12
+                             -A
 
       - name: Clean up temporary certificate file
         if: ${{ always() }}
@@ -72,7 +77,7 @@ jobs:
           persist-credentials: false
 
       - name: Get Homebrew version from Git
-        id: print-version
+        id: homebrew-version
         run: echo "version=$(git -C brew describe --tags --always)" >> "${GITHUB_OUTPUT}"
 
       - name: Copy Homebrew API cache to brew subdirectory
@@ -86,23 +91,54 @@ jobs:
         # binaries so it needs to be excluded from notarization.
         run: pkgbuild --root brew
                       --scripts brew/package/scripts
-                      --identifier "sh.brew.homebrew"
-                      --version ${{ steps.print-version.outputs.version }}
-                      --install-location "/opt/homebrew"
+                      --identifier sh.brew.homebrew
+                      --version "${{ steps.homebrew-version.outputs.version }}"
+                      --install-location /opt/homebrew
                       --filter .DS_Store
                       --filter "(.*)/Library/Homebrew/test/support/fixtures/"
-                      --min-os-version "${MIN_MACOS_VERSION}"
-                      --sign "${PKG_APPLE_DEVELOPER_TEAM_ID}" Homebrew.pkg
+                      --min-os-version "${HOMEBREW_MACOS_OLDEST_SUPPORTED}"
+                      --sign "${PKG_APPLE_DEVELOPER_TEAM_ID}"
+                      Homebrew.pkg
 
       - name: Convert Homebrew license file to RTF
         run: (printf "### " && cat brew/LICENSE.txt) |
               pandoc --from markdown --standalone --output brew/package/resources/LICENSE.rtf
 
-      - name: Build Homebrew installer package
+      - name: Build Homebrew installer product package
         run: productbuild --resources brew/package/resources
                           --distribution brew/package/Distribution.xml
-                          --package-path Homebrew.pkg Homebrew-${{ steps.print-version.outputs.version }}.pkg
+                          --package-path Homebrew.pkg
                           --sign "${PKG_APPLE_DEVELOPER_TEAM_ID}"
+                          Homebrew-${{ steps.homebrew-version.outputs.version }}.pkg
+
+      - name: Clean up temporary macOS keychain
+        if: ${{ always() }}
+        run: |
+          if [[ -f "${RUNNER_TEMP}/${TEMPORARY_KEYCHAIN_FILE}" ]]
+          then
+            security delete-keychain "${RUNNER_TEMP}/${TEMPORARY_KEYCHAIN_FILE}"
+          fi
+
+      - name: Upload installer to GitHub Actions
+        uses: actions/upload-artifact@v3
+        with:
+          name: Homebrew-${{ steps.homebrew-version.outputs.version }}.pkg
+          path: Homebrew-${{ steps.homebrew-version.outputs.version }}.pkg
+  test:
+    needs: build
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      matrix:
+        include:
+          # Intel (free)
+          - runner: macos-latest
+          # Apple Silicon (paid)
+          - runner: macos-latest-xlarge
+    steps:
+      - name: Download installer from GitHub Actions
+        uses: actions/download-artifact@v3
+        with:
+          name: "${{ needs.build.outputs.installer_path }}"
 
       - name: Remove existing Homebrew installations
         run: |
@@ -114,7 +150,7 @@ jobs:
         run: echo | sudo tee /var/log/install.log
 
       - name: Install Homebrew from installer package
-        run: sudo installer -verbose -pkg Homebrew-${{ steps.print-version.outputs.version }}.pkg -target /
+        run: sudo installer -verbose -pkg "${{ needs.build.outputs.installer_path }}" -target /
 
       - name: Output installer logs
         if: ${{ always() }}
@@ -128,7 +164,7 @@ jobs:
         run: echo | sudo tee /var/log/install.log
 
       - name: Reinstall Homebrew from installer package
-        run: sudo installer -verbose -pkg Homebrew-${{ steps.print-version.outputs.version }}.pkg -target /
+        run: sudo installer -verbose -pkg "${{ needs.build.outputs.installer_path }}" -target /
 
       - name: Output installer logs (again)
         if: ${{ always() }}
@@ -138,37 +174,35 @@ jobs:
 
       - run: brew doctor
 
+  upload:
+    needs: [build, test]
+    runs-on: macos-latest
+    permissions:
+      # To write assets to GitHub release
+      contents: write
+    steps:
+      - name: Download installer from GitHub Actions
+        uses: actions/download-artifact@v3
+        with:
+          name: "${{ needs.build.outputs.installer_path }}"
+
       - name: Notarize Homebrew installer package
         env:
           PKG_APPLE_ID_EMAIL: ${{ secrets.PKG_APPLE_ID_EMAIL }}
           PKG_APPLE_ID_APP_SPECIFIC_PASSWORD: ${{ secrets.PKG_APPLE_ID_APP_SPECIFIC_PASSWORD }}
-        run: xcrun notarytool submit Homebrew-${{ steps.print-version.outputs.version }}.pkg
+        run: xcrun notarytool submit "${{ needs.build.outputs.installer_path }}"
                                     --team-id  "${PKG_APPLE_DEVELOPER_TEAM_ID}"
                                     --apple-id "${PKG_APPLE_ID_EMAIL}"
                                     --password "${PKG_APPLE_ID_APP_SPECIFIC_PASSWORD}"
                                     --wait
 
-      - name: Clean up temporary macOS keychain
-        if: ${{ always() }}
-        run: |
-          if [[ -f "${RUNNER_TEMP}/${TEMPORARY_KEYCHAIN_FILE}" ]]
-          then
-            security delete-keychain "${RUNNER_TEMP}/${TEMPORARY_KEYCHAIN_FILE}"
-          fi
-
-      - name: Upload installer to GitHub Actions
-        uses: actions/upload-artifact@v3
-        with:
-          name: Homebrew ${{ steps.print-version.outputs.version }}
-          path: Homebrew-${{ steps.print-version.outputs.version }}.pkg
-
       - name: Install gh
         run: brew install gh
 
       - name: Upload installer to GitHub release
-        if: startsWith(github.ref, 'refs/tags/')
+        if: github.event_name == 'release'
         env:
           GH_TOKEN: ${{ github.token }}
         run: gh release upload --repo Homebrew/brew
-                               "${GITHUB_REF//refs\/tags\//}"
-                               Homebrew-${{ steps.print-version.outputs.version }}.pkg
+                                "${GITHUB_REF//refs\/tags\//}"
+                                "${{ needs.build.outputs.installer_path }}"
diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 77af0a0b48..38bfd0e26e 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -510,7 +510,8 @@ esac
 HOMEBREW_MACOS_NEWEST_UNSUPPORTED="15"
 # TODO: bump version when new macOS is released and update references in:
 # - docs/Installation.md
-# - MIN_MACOS_VERSION in .github/workflows/build-pkg.yml
+# - HOMEBREW_MACOS_OLDEST_SUPPORTED in .github/workflows/installer-package.yml
+# - `os-version min` in package/Distribution.xml
 # - https://github.com/Homebrew/install/blob/HEAD/install.sh
 HOMEBREW_MACOS_OLDEST_SUPPORTED="12"
 HOMEBREW_MACOS_OLDEST_ALLOWED="10.11"
diff --git a/package/Distribution.xml b/package/Distribution.xml
index 8c8fb12c18..2c479d44cd 100644
--- a/package/Distribution.xml
+++ b/package/Distribution.xml
@@ -4,7 +4,7 @@
   <options customize="never" hostArchitectures="x86_64,arm64" rootVolumeOnly="true"/>
   <volume-check>
     <allowed-os-versions>
-        <os-version min="11.0.0"/>
+        <os-version min="12.0.0"/>
     </allowed-os-versions>
   </volume-check>
   <choices-outline>
@@ -27,7 +27,7 @@
   <license file="LICENSE.rtf"/>
   <conclusion file="CONCLUSION.rtf" />
   <allowed-os-versions>
-    <os-version min="11.0"/>
+    <os-version min="12.0.0"/>
   </allowed-os-versions>
 
   <script>
diff --git a/package/scripts/postinstall b/package/scripts/postinstall
index 8d9f1c22d0..d3a5710a68 100755
--- a/package/scripts/postinstall
+++ b/package/scripts/postinstall
@@ -3,7 +3,7 @@
 # $2 Location of the Homebrew installation we may need to move into place
 # $3 Target install location (unused)
 # $4 System root directory (unused)
-set -eu
+set -euo pipefail
 
 # disable analytics while installing
 export HOMEBREW_NO_ANALYTICS_THIS_RUN=1
@@ -26,24 +26,33 @@ cd "${homebrew_directory}"
 git config --global --add safe.directory "${homebrew_directory}"
 git reset --hard
 git checkout --force master
-git branch | grep -v '\*' | xargs -n 1 git branch --delete --force
+git branch | grep -v '\*' | xargs -n 1 git branch --delete --force || true
 git config --global --unset safe.directory "${homebrew_directory}"
 
 # move to /usr/local if on x86_64
 if [[ $(uname -m) == "x86_64" ]]
 then
-  sudo mkdir -vp /usr/local/bin /usr/local/Homebrew
-  cp -a "${homebrew_directory}"/* "${homebrew_directory}/".??* "/usr/local/Homebrew/"
+  if [[ -f "/usr/local/bin/brew" && -d "/usr/local/Homebrew" ]]
+  then
+    cp -pRL "${homebrew_directory}/.git" "/usr/local/Homebrew/"
+    mv "${homebrew_directory}/cache_api" "/usr/local/Homebrew/"
+    git -C /usr/local/Homebrew reset --hard
+    git -C /usr/local/Homebrew checkout --force master
+  else
+    mkdir -vp /usr/local/bin
+    mv "${homebrew_directory}" "/usr/local/Homebrew/"
 
-  # create symlink to /usr/local/bin/brew
-  ln -svf "../Homebrew/bin/brew" "/usr/local/bin/brew"
+    # create symlink to /usr/local/bin/brew
+    ln -svf "../Homebrew/bin/brew" "/usr/local/bin/brew"
+  fi
 
+  rm -rf "${homebrew_directory}"
   homebrew_directory="/usr/local/Homebrew"
   cd /usr/local
 fi
 
 # create missing directories
-sudo mkdir -vp Cellar Frameworks etc include lib opt sbin share var/homebrew/linked
+mkdir -vp Cellar Frameworks etc include lib opt sbin share var/homebrew/linked
 
 # set permissions
 logged_in_user=$(echo "show State:/Users/ConsoleUser" | scutil | awk '/Name :/ { print $3 }')