So much for semver. This should be a breaking change warranting an Xcode 12 major version.
But you're not allowed to submit apps to the stores with unofficial toolchains.
IIRC, the toolchain checks the versions of SDKs shipped in the installed Xcode and refuse to compile your source code if anything's not up to date.
> But you're not allowed to submit apps to the stores with unofficial toolchains.
Not sure this is true. Apple does not allow you to copy/run Xcode from non-Apple hardware. Other than that, submitting an app built with an OSS toolchain should be fine.
https://developer.apple.com/library/archive/documentation/To...