I get this Pop Up now. How do I fix this? Thank you
You can open the folder in question to see if there's a "Can't write" icon (a pencil with a line through it) in the lower left hand corner of the window. If there is, "Get Info" on the folder and, in the permissions section, try to give your username Read/Write permissions (you may have to unlock the lock first). If that doesn't work wait until there's a version of Onyx for Catalina, and run that to fix permissions.