Edited .psb file can no longer be opened

Thank you very much for the additional information and suggestions.

Best wishes from Berlin, Chris

OK - in that case you may have a bigger problem that you really should take seriously. Layer corruption should not happen, ever. That's a symptom of failing hardware!

Are you saving directly to external drives? That is something you should never do. Save to local drive, then copy over. Worn and loose cables and connectors are always a risk. Replace the cables regularly. Never touch the drive when data transfer is in progress!

This is always an issue with laptops and Macs, where you can't add internal storage space. If you work with images you will run out sooner or later, it's just a matter of time. So you need a strategy for handling external storage.

Thank you for your answer!!! The solution was to duplicate all single layers (because some of them were corrupted) and copy them step by step into a new file. Now it works:-)

I don't do Mac, but since no one else has answered - this sounds like you haven't set the proper permission levels. This has apparently become much stricter in newer MacOS versions.