I use my airpods with my graphene os device (also a 7a) every day. One thing I'd recommend doing is first connect the airpods to a macos/iOS device and go into settings to customize the double tap/squeeze options for your airpods. This will then be the behavior those actions will have with your graphene device. Then have all apple devices forget those airpods.
Once that's done you should be able to have your 7a find and connect to the airpods once you put them as n pairing mode.