I've got a feedback reply from Apple asking to re-check it on macOS 11.4 GM. Can't check it there however the issue is definitely resolved on macOS 11.5 Beta.
Hopefully they will merge this fix later. It sucks that I had to re-do whole app without Lists...
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Apple has fixed it, works as intended on macOS 11.5 Beta.
Bug #FB8955055
Hello @Tylor,
It works as intended on iOS. It crashes on macOS. Did you try that on a macOS target?
Filed a bug report #FB8965816.
The crash remains if there are children in items and you delete the last item.
Exactly the same code works as intended on iOS.