I was alerted that some folks who rebuilt their Mac apps with Xcode 15 are finding they crash at launch on M1 Macs running Big Sur. I just happen to have such a beast at my disposal, and I reproduced likely the same crash on it with MarsEdit. It looks like some boilerplate dyld initialization that is compiled in expects libc++ to be loaded, but it’s not… not sure if any developers can easily work around it. Probably an Apple job.