I had some issues with running PyMC (versions 5.6.1 and 5.16.2) after updating macOS and Xcode only (to version 15.4). I am still on macOS 14 Sonoma.
I agree with @twiecki that clang++ of PyMC is pointing to the wrong version. It should be pointing to the one with Xcode installation. I agree with @Werdna48 that the issue is with Xcode
This is the weird thing that happened after I upgrade Xcode.
I tried this in my Terminal:
xcodebuild -version
and I got this error
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
If anyone has this same error like me, what you should do is to follow this article here: macos - xcode-select active developer directory error - Stack Overflow
Enter this line of code into your Terminal to point your clang++
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
This will point Xcode (and clang++) to the correct folder.