APFS vs Mac OS Extended (Journaled) for Time Machine Backup on external HDD Which one between APFS and Mac OS Extended (Journaled) performs better as partition store type for Time Machine backup in an external HDD (Magnetic Storage over USB connectivity)?
Note this answer now depends on the version of OSX/macOS you have.
This answer is  for macOS Catalina and earlier versions - Big Sur now can use APFS - see  Apple's Types of disks you can use with Time Machine on Mac You can also use HFS+ as before.
You can't use APFS as a Time Machine target:
https://support.apple.com/en-us/HT202784#format
Time Machine drives must be HFS+. That will likely change in the future but currently it is HFS+ only.