Import failed to save. There was an internal error attempting to save this import. The changes made were not saved.

Hello Animaaaaal,

Thanks for that info and for choosing the Apple Support Communities. If I understand correctly, you are unable to accept a Calendar invite on your Mac, as you get an error message. To help isolate this, use safe mode to start up your Mac as it does the following things:

• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files

Log in to your user account and test the issue while in safe mode and then restart normally and test the issue again.

Use safe mode to isolate issues with your Mac

Graphics performance limited in macOS Recovery, safe mode, or Guest User mode

Cheers!