Apple’s just-released macOS Monterey 12.3.1 or its Apple Studio Display Firmware Update 15.4 has “bricked” my Apple Studio Display.
As shown in the graphic, the display just turns on with a monitor icon and an exclamation mark. Neither disconnecting my MacBook Pro or unplugging and replugging the display has rectified the situation.
Update: after numerous self-implemented restarts the Studio Display is now working fine. Not sure what cause the issue and why repeated power-ups were necessary, but, well, there you go.