This worked for me, same problem, wouldn't work on the 12 but would work on other devices ... after a chat with a very nice Apple support person, this got sent up to phone support and the phone support person didn't even know why this worked, she was troubleshooting for a different potential issue lol... but I'll take it!
1) Connect to AirPods, with both of them in your ears
2) Take one AirPod out, place it in the case. Play music in Music app. Is the one in your ear working now?
3) If yes, switch to the other AirPod. Is it working too? Yes?
4) Now place them back in the case, and then put them back in your ears. Are they both working now?
If they are, you got lucky like I did!
I swear I had done every single usual suggestion given for getting them to work again. This solution needs to be added to the list!