I replaced the ssd in my mbp. Rather than simply restore from time machine, I reformatted and did a fresh install of Mojave 10.14, I like to start from scratch every so often and this seemed like a good time.
The computer is backed up via an unencrypted TM backup on an encrypted backup volume, which is an HFS+ volume on a HDD connected via USB.
Now I want to preserve the old TM backup, and start a new TM backup on the same disk. I want the backup to not be encrypted, and the backup volume to remain encrypted.
So I went to TM preference pane, click "select disk", click the volume, uncheck "encrypt backups", click "use disk." The OS throws up a modal that says "The password for the disk "DiskName" is required to turn off encryption." When I fill in the text box, the button "Turn off Encryption" becomes avaialable.
Again, the existing TM backup is not encrypted.
What happens if I click Turn off Encryption? And how can I get from here to where I want to be, with a volume that IS encrypted, and a backup that IS NOT encrypted?