We have a project that has issues with Xcode 16. It requires Xcode 15.4, which no longer runs on Sequoia.
It looks like this is prevented by a plist entry and Gatekeeper at first launch. Here is the workaround. It also works with Xcode 14.
1. Download Xcode 15 from the Developer Portal or copy Xcode 15.4 from another installation. I named mine Xcode_15.app in /Applications.
2. 'Show package contents' from an Xcode 16 install and copy its info.plist.
3. 'Show package content' of the Xcode_15.app and rename its info.plist to something like info15.plist.
4. Move the info.piist you copied into the bundle and close it.
5. Launch Xcode_15.app and let it initialize..
6. You can now close it and revert the info15.plist. I renamed the copied info.plist to info16.plist and keep it around in case Gatekeeper has a fit or I want to move or copy the old Xcode.
It is great not to need Sonoma around just to run the old Xcode. On Apple Silicon, you cannot use a VM, since Sonoma does not let you log in to the portal.
It looks like this is prevented by a plist entry and Gatekeeper at first launch. Here is the workaround. It also works with Xcode 14.
1. Download Xcode 15 from the Developer Portal or copy Xcode 15.4 from another installation. I named mine Xcode_15.app in /Applications.
2. 'Show package contents' from an Xcode 16 install and copy its info.plist.
3. 'Show package content' of the Xcode_15.app and rename its info.plist to something like info15.plist.
4. Move the info.piist you copied into the bundle and close it.
5. Launch Xcode_15.app and let it initialize..
6. You can now close it and revert the info15.plist. I renamed the copied info.plist to info16.plist and keep it around in case Gatekeeper has a fit or I want to move or copy the old Xcode.
It is great not to need Sonoma around just to run the old Xcode. On Apple Silicon, you cannot use a VM, since Sonoma does not let you log in to the portal.