Which format should I choose for a Time Machine backup volume? I'm using Catalina on an formatted APFS SSD and am finding a correct way to backup the OS. In the plugged in external HDD, I create a backup volume with APFS format using Disk Utility. But when I choose it as the backup volume in Time Machine, Time Machine requires the volume have to be erased. I did it and then go to Disk Utility to check, the volume is now formatted as Mac OS Extended (Journaled).
Should I continue to use it? Will it occur any problems when I make a restore from backups on a Mac OS Extended (Journaled) to an APFS SSD? Thanks for any help.
Time Machine in Catalina only supports HFS+ as a destination volume.  The first macOS that supports APFS as a destination volume is Big Sur.
ref:
https://support.apple.com/guide/mac-help/types-of-disks-you-can-use-with-time-machine-mh15139/10.15/mac/10.15
vs:
https://support.apple.com/guide/mac-help/types-of-disks-you-can-use-with-time-machine-mh15139/11.0/mac/11.0