Joplin 2.8.8 on Mac, trying to set up an existing sync from OneDrive. Unfortunately, Joplin doesn't allow me to enter password to actually decrypt anything.
Do you have any extended ascii characters in your password? If so, it is being tracked in issue #6005. If this is your issue, please do make a comment there so the devs are aware that it is still an issue. It is not being worked on as far as I'm aware.