Well, for instance https://developer.apple.com/documentation/xcode/identifying-the-cause-of-common-crashes says If the Swift runtime encounters a programming error, the runtime catches the error and intentionally crashes the app. But again the question is, if this is really a programming error on my side, how do I find it?

That suggests that you’re hitting the issue described in Updating Mac Software, or something like it. That's weird. My apps do include a software updater (Sparkle) for the versions I sell on my website, but for the App Store versions, the updater is not included. I have separate Xcode targets for the two versions, and the App Store target (the one for which Xcode downloads the crash reports) doesn't even link to the updater. And when running the apps locally (including when the only crash on my Mac happened, which wasn't in Xcode, but just launching the debug build from Spotlight), I always run the App Store version.

Thanks, I'll do that, although I'm not very hopeful that I'll get the crash again soon (while I've been observing the crash reports downloaded by Xcode for many months). Just to be clear, should I then extract the sysdiagnose and look in the system_logs.logarchive file? In the sysdiagnose I uploaded to Feedback Assistant I can only see the last 5 minutes, is that correct?