Ich kann die gestern gespeicherte Datei nicht mehr öffnen. Es kommt immer die Fehlermeldung Datei konnte nicht geöffnet werden.
You have to share your model file if you want us to be able to investigate..
More often than not, files that do this can’t be saved. Occasionally, components within the file can be recovered. The best solution is try the back up file that is saved with the original (~.skp on Mac, .skpb on windows?) or if you have other file backup to revert to. Apple’s Time Machine backups are good for this, but I’m not I’m not on Windows and don’t know what’s available there.
It isn’t known definitively why this happens; saving to a cloud storage is strongly suspected but not definitely the reason.