Machine reverted to Ventura

Something weird has happened to my machine. It says it is running Ventura. But I had upgraded to Monterey some time ago. If I go to Software update there is no Monterey option, just a later version of Ventura.

A Monterey disk icon appears on my desktop after startup (separate from Macintosh HD). If I open this it's empty. If I eject it it it says Preboot wasn't ejected, if I force that then it says Update wasn't ejected, then finally forcing that says VM wasn't ejected. That gets rid of it until the next restart.

Has anyone any idea what is going on.

I clearly lost the plot!!

Machine reverted to Ventura
 
 
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