Time Machine on Ventura 13.7.5 does not recognise attached external Z666 enclosure

I am rebuilding a 2019 intel iMac with an external Z666 4TB Zike drive attached via TB3 port.

Main drive is Ventura 770 (13.7.5) Also internal secondary drive Samsung Evo 870 with clone of Ventura 770

I am trying to setup TM but TM cannot find external drive. Z666 is set up as a boot drive with Ventura 13.7.5. onto which I expected to create TM partition Ventura 770 TM

In earlier OS versions I had no problem. I could step back but to earlier version but I feel sure there must be a rational answer to the problem. Apple User Guide does not help. I have tried unplugging then re plugging external drive to prompt ‘Do you want to use this disk as a Time Machine backup disk’ Does not happen.

Help would be appreciated.

OK Guys,

Solved the problem. I create a TM drive BEFORE creating disk partitions!

What a Klutz!