TimeMachine backup broken after upgrading

After recently upgrading my Mac, TimeMachine started suggesting that it had verified the integrity of the backup and that I needed to start a new backup. I have my backup on a NAS mounted as afs on my Mac. However, when I looked at the files in the backup, macOS had renamed my TimeMachine backup to .purgeable.sparsebundle. When I looked in the directory, there were no files except the bands directory. Now it seems the bands still exist but none of the plist files exist. I accidentally started a new backup and I am not sure if that deleted these files and renamed the sparsebundle but regardless, I don't have the files. I then proceeded to copy over the plists from the new backup to this directory and tried to follow the tutorial here. However, when I execute hdiutil attach command, I see the following output -

hdiutil attach -nomount -noverify -noautofsck /Volumes/Backups/djmbp.sparsebundle
/dev/disk2              GUID_partition_scheme
/dev/disk2s1            EFI

The volume is missing. Help appreciated!

The problem with "… Time Machine must create a new backup …" is an old annoying one, see one of many discussions on apple, from 2016. Apple doesn't seem to be interested. You did well in finding a good tutorial on jd-powered.net.

However, as you wrote you accidentally started a new backup, that will have deleted all the old backups. When I had the recurring problem in 2016 and 2017 I moved the whole old backup over from my time capsule to a spare disk before restarting a new Time machine backup. Moving them over wired Ethernet took days, literally. (Btw: I am not too sure that my old safeguarded backups are still usable.)