iMac bricked after last OS X Catalina supplemental.

i installed a new tablet yesterday, and after unplugging it for cleanup, I saw I software update supplemental available.

I clicked and the iMac restarted, and I just left running while cleaning the tablet, eventually going to bed. About 20 minutes ago, after getting up for a glass of water, I jiggled the mouse to see the status of the update. The iMac didn’t wake up, so I clicked and hold the power button, nothing. Several tries later, still nothing.

Should be ragin ****** about it, but I just said “oh well, my turn in the barrel”. So... How do you unbrick an iMac after a failed update?. Any solutions will be appreciated.

Danke in advance