Is it redundant to select encryption in Time Machine if the disk partition was created as encrypted?
Is that why it's taking days for Time Machine to encrypt my initial backup?
(Mohave)
iMac 21.5", macOS 10.14
Yes, it is re-encrypting the drive. Since there is data on the drive, it is doing a lot of moving stuff around.
Time Machine should have a dedicated drive. If you have to partition a drive to share with TM, the TM should always be the 1st partition to keep the confusion down—allowing TM to always be able to find the drive.
Keep your Time Machine backup disk for Mac secure - Apple Support
Choose a backup disk and set encryption options on Mac - Apple ...
Back up your Mac with Time Machine - Apple Support
3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.
Time Machine encryption slow on an encrypted partition
