Time Machine

Just what it says, it is not configured. However it might be an error. Begin by restarting in Safe Mode with all wired peripherals disconnected (including your TM EHD) and then restart normally and test Time Machine. You can learn how to do a Safe Mode restart in Safe Mode Reset

That means you have not configured Time Machine...

https://support.apple.com/en-us/HT201250

If you *have* configured time machine, it means that your backup is corrupted.

My thoughts on backup disks are the same as my rule on underwear: It it's doubtful, it's dirty.

I would throw away this disk, get another one, format it APFS and start fresh.