Update: I tried these instructions: https://raspberrypi.stackexchange.com/questions/53408/automatically-connect-trusted-bluetooth-speaker/76288#76288
Installed BaReinhard's repo and rebooted. I was able to connect to the AirPods when it launched back up and for a brief moment sound actually came through from youtube on the AirPods and I thought I may have fixed it, but then it cut out again after about two seconds. I'm getting the feeling that it connects and then gets disconnected almost immediately for some reason. Indeed, looking at bluetoothctl it seems to connect then disconnect to the devices immediately.
E.g. it will say:
sudo bluetoothctl
Agent registered
[CHG] Device D0:03:4B:ED:E5:20 Connected: yes
[CHG] Device D0:03:4B:ED:E5:20 Connected: no
[CHG] Device D0:03:4B:ED:E5:20 Connected: yes
[CHG] Device D0:03:4B:ED:E5:20 Connected: no
in quick succession, continuing on with this "yes/no" pattern. It does not seem able to maintain a connection.
Don't know if that sheds any light on the problem.