Unable to include external media drive in time machine backup

Question

I have recently moved my apple photo library to an external hard drive to save space on my internal SSD, however i would obviously still like this external drive to backup with the rest of my computer. However it appears i am unable to take this drive off the excluded list (as shown below), does anyone know how i can remedy this?

Cheers.

Answer 1

Best guess is the drive is the wrong format.
Time Machine won't back up NTFS, FAT or ExFAT.

APFS should work, but 'safest' is HFS+ [MacOS Extended, Journaled] using GUID, not MBR. These options are available in Disk Utility.
You will not be able to change the format "live," you will need to copy this data elsewhere, then erase the drive & then copy back to it afterwards.