Due to a complicated series of events, I have a right AirPod Pro and a left AirPod non-pro. Surprisingly, I had no trouble pairing them to my iPhone and getting it to play into both of them simultaneously. However, for my computer (MacBook Air) it's been more difficult.
The internet told me that I should go to Audio MIDI Setup and create a Multi-Output Device with both of them. I was able to create a multi-output device, and attach my AirPod Pro. However, I wasn't able to add the AirPod non-pro - my computer has recognized it exists, but every time I press "Connect", it flickers to "Connected" and then goes back to "Not connected." Since it's allegedly not conected, I can't add it to my multi-output device.
When I first tried this the other day, I was able to connect my AirPod non-pro, but whenever I connected it, the Airpod Pro would become disconnected - so I could never have them connected at the same time.
Anyway, I'll assign M$1000 to anyone who successfully helps me get my two separate AirPods connected to my Mac. If multiple commenters deserve partial credit, I will split the mana according to the importance of their contributions.
General policy for my bounty markets: In the rare event of a conflict between my stated criteria and the agreed-upon common-sense spirit of the bounty market, I may pay out funds according to the bounty market's spirit or not at all.