Western Digital Passport for Mac

I need to ask if there are any known problems using WD Passport with Big Sur 11.4. When I look into System report I can see the Passport is connected, and is the same when I look in Disc Utility. I also check the drive status in WD security and it passes the status test. But when I press Back Up Now in Time Machine I get the message the disc is not available and under more info it says it is not connected.

I have tried different cables and different USB ports to no avail.

This is the 2nd Passport from Western Digital. The first one backed up a few times before becoming eratic

and the packed up altogether. There had been a few OS updates between first use of the Passport and it failing. WD replaced the drive which came all the way from Poland to the UK

I first bought a Passport to use with a Mac Mini some years ago and it worked a treat. I am puzzled as to why this is giving such grief.