That last #SteamDeck update really borked my system. I had to do the same fix that I have always had to do. I don't know why it works, but it does.
I had to open it up & unplug the battery cable & then plug in the AC adapter & turn on the system. Once it booted up then I had to shut it down. Remove the AC adapter. Plug the battery back in & put it back together.
It's been awhile since I've had to do this but I have had to do it a half dozen times over the last several years.