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I found this link. It says that even though TM deletes old backups, you might run out of space on the drive.
https://support.apple.com/guide/mac-help/if-the-time-machine-backup-disk-is-full-mh15137/mac
I too thought I would never run out, but be asked that I might have to delete some information from older backups.
Are you sure the message is just not telling you that it has run out of space and thus will be deleting older information? I have gotten the message I just described, and it scares you/me.
If indeed for some reason you can't get TM to work on this drive: You could re-format the drive and start all over with a new, first time, backup (which will take quite some time). Another suggestion is to get a new drive and make a new backup. Eventually the first drive will die, at least this way you start its replacement before the old one dies.
It didn't say that it will be deleting older information, it just says that there's not enough space on the disk.
Time Machine was for "version control" of a single file over "time". This can accumulate a large amount of data if that file changes often, or it has been years of backups.
If you are happy with the "current backup", you can do a combination of the support articles steps to "exclude" your drive, at which point it will delete all versions of the backup, and you then remove the exclusion the harddrive so that it will be backed up again.
Otherwise you can do that to specific directories within your user directory to remove revisions, and then remember to remove the directory so that backups continue.
Additionally, you may find that you want to "exclude" some hard drives from being backed up if they are external. Time Machine will try to backup EVERYTHING it can unless it is excluded. Good luck!
Settings > Time Machine > Options