Hi,
I use the backup plugin (interval 1h, keep 1 backup) and every now an then Joplin shows me this message:
(correct path info blinded for screenshot)
I don't understand that message. All I can see is, that the backup I have on my HDD is older than 1 hour, so I can say the last backup process might have been unsuccessful.
Is it an external or network drive by chance? They could have all kinds of weird issues
Try choosing another target directory, this one you're using seems to have restrictions on writing. Best option to start with is inside current user folder say ~/Documents . After successful attempt you may try more complicated paths like shared folder with a password, network drive, mounted cloud etc