Volume is wrong format for a backup

The Time Machine backup format with Catalina through Sequoia is entirely different than it was for Mojave and earlier.

You do not copy Time Machine backups between drives. You do start a new APFS formatted drive with Sequoia that is sized 2.5 - 3x of your internal Mac storage. I use a 2 TB Crucial X9 SSD with a USB-C 3.2 Gen 2 rated cable into a TB4 or USB-C port depending on the Mac.

Same situation here, TM started running Sequoia, drive failed and can't be repaired. I get a pop-up when the failed disk is mounted noting: "You can still open or copy files on the disk, but you can’t save changes to files on the disk. Back up the disk and reformat it as soon as you can" yet there seems no way to back up this data, and even if I could, how would I access it if it isn't part of my TM setup?

When trying to copy "backups.backupdb", or any files within, I get the same error as EricWeir above. DiskUtil shows my older TM has "File system : Mac OS Extended" and not the actual drive format or HFS+ issues noted elsewhere online. New TM backup is APFS of course.

If I just have to start anew from here I can reluctantly accept that but worry that my previous backups going back 4 years might end up as inaccessible...