With Monterey I recommend formatting all attached drives, SSD or hard drive, as APFS, especially in the case of Time Machine drives.
I have four 8-TB hard drives consisting of 11 volumes, all APFS; and four SSDs of 13 volumes, APFS as well. The only external drive I have in HFS+ format is my USB SSD used for installing macOS. Somehow, you cannot use APFS for a bootable, self-contained macOS installer.