Time Machine can't use old but unused drive

I already followed that procedure when I first connected the disk. It came set up in ExFAT with a Master Boot Record, which is pretty much useless for using with a Mac. I gave it a GUID Partition Map and initially formatted it HFS+.

According to the package and manual, it is compatible with Intel Mac hardware (which my 2019 MBP has). But since it dates from 2012, the newest macOS listed in the system requirements is 10.4. It says it's compatible with 10.4 or newer, but considering how much has changed since then, that doesn't really say anything useful about its compatibility with more current OSes. I will say that the drive gives me no trouble unless I try to set it as a TM disk or format it as APFS. It comes through First Aid clean, both the drive and the volume, as GUID/HFS+. I have saved files to it and read them back without issues. So if it's incompatible, it's specifically with either APFS or TM in a newer OS, not with the Mac in general or Big Sur in general.

I will also mention that my old TM drive was HFS+, not APFS, and I had no troubles using it as a TM disk or migrating my TM backups from its predecessor. My internal SSD is APFS, of course.

I tried that twice, first by erasing just the volume, then the entire disk. I got the following response:

Erasing “Hitachi Hitachi HDS722020ALA330 Media” (disk6) and creating “TM”

Unmounting disk
Creating the partition map
Waiting for partitions to activate
Formatting disk6s2 as Mac OS Extended (Journaled) with name TM
Initialized /dev/rdisk6s2 as a 2 TB case-insensitive HFS Plus volume with a 155648k journal

Mounting disk
Creating a new empty APFS Container
Unmounting Volumes
Switching disk6s2 to APFS
Creating APFS Container
tx_flush:1063: rdisk6s2 xid 1 sync/barrier failed: 5
tx_mgr_free_tx:208: rdisk6s2 Trash unfinished pending tx, xid range = 0x1 - 0x1
newfs_apfs: unable to format /dev/disk6s2: Input/output error
failed to finish first transaction: 5 - Input/output error

An internal error has occurred. : (-69626)

Operation failed…

Searching on that error message turned up nothing useful I could understand. It was a good idea, though. I'm open to more suggestions.

At this point, I've already determined that the old TM drive isn't salvageable—it will mount as read-only, but it has enough bad blocks that I can't trust it reformatted—so I've already ordered a replacement drive that I should be receiving tomorrow. After almost a week without any active TM backups, another day or two won't make much difference. Once I have the replacement drive, I'll see if I can merge the read-only data into a new TM backup set. But I do appreciate the additional info. I'll probably try DriveDx later, just to see if the drive is actually trustable for anything.