I just had this happen with the 12.4.1 update. Blinky LED & no video out at all. The bad news is the Genius Bar / Store Techs have no more access to do a factory restore than the user does. IOW: none. Nothing on Ethernet either. (That was straight from the GB guy’s mouth.) If there are USB pads on the board they don’t know about them.
And if this happens out of warranty it’s a $150 board swap. I advise turning off the auto-install for OS updates.