It seems that the problem is fixed in LLVM 16.0.2 - https://discourse.llvm.org/t/llvm-16-0-2-release/70107 I can still follow up if needed for a bug report. I was having problems getting a reproducer because the command line tool did not support -flto=thin, now it does so I could perhaps now if needed.

I finally filed a new bug - before scala-cli did not support the LTO thin option so the reproducer would have been involved. Now it should only take a few minutes. https://feedbackassistant.apple.com/feedback/17746484

I finally filed a new bug. Now the reproducer is easier and should only take a few minutes. https://feedbackassistant.apple.com/feedback/17746484