Cannot save files and folders to backup drive
I have a 2TB USB external backup drive that is formatted with APFS and encrypted connected to a Mac Pro 2013. I use it for Time Machine backups using OS X Monterey. Now I noticed that I cannot create new folders or save any files to the external backup drive. i.e. it is only good for running automatic Time Machine backups and nothing else. i.e. the New Folder icon is greyed out in Finder menu if I select the external USB drive. More than half the drive is empty space since my Mac Pro 2013 only has a 1 TB SSD drive. What are the rules for configuring external drives so that they can be used for both Time Machine Backups and saving ordinary files and folders? I seem to remember that earlier backup disk configurations allowed one to also drag and drop files and folders. Has something changed?