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
without pubg popping off, fortnite wouldn't add battle royale, and call of duty wouldn't go even shittier than it did before because of blackout, warzone and dmz