Problem Using New Apple Studio Monitor as Second Monitor

Yesterday I bought a new 27-inch Apple Studio monitor to be my second monitor with my Mac Studio, replacing an ancient Cinema Display. My first monitor is also a 27-inch Studio monitor. They were working perfectly. This morning, after a while the mouse stopped being able to move over to the second monitor and I couldn't move windows from the first monitor to the second.

A few minutes later I got an update message that there's a software update for the new monitor. I installed the update, but still no use of either monitor as a second monitor. Both monitors are still turned on and displaying the background wallpaper showing on whichever monitor I designate as the second monitor via DIsplays in the Settings box.

Any ideas what's going on and what I can do to be able to have the second monitor as expanded screen real estate as before?

Steve Tiano