I had the same issue, with the physical orientation of the switch being important (lying face down on the bench, it mostly worked). Likely due to the dat0 adaptor having only partial contact.
Solved it by doing kamikaze.
Plug it into a computer and use putty to get the error code.
Also consider it might actually be using hwfly diagnostics:
https://gbatemp.net/threads/switch-oled-modchip-blinking-red-and-not-launching.628523/#post-10100691
Caller -"Everytime I start a Pc game on my S24, playing on a external monitor, someone calls or texts me, n it kicks me out of the game." Customer Support - Click (hangs up)
I found it funny cause many many years ago, had a roommate in college that did this same dumbass branding of the school logo, but it didn't look anything like it after it healed. Just looked like a birthmark.