Time Machine backup disk formation under 10.15 what format to use?

I use an external disk on a network connected Mac Mini to do the TM backups of the other Mac’ in the network. I will soon upgrade all machines to 10.15 and like to know what format the disk should be we are backing up to.

In the past, before APFS, the disk was formatted as Mac OS Extended (Journaled) with a GUID Partion map, is this still so? And next does it need a GUID Partion map, like I always did, or one of the other two? Or does TM need an APFS Container? Or does it not matter?

Thanks.