He doesn't need to wrestle. He doesn't even need to manage. He can be a part time special attraction.
New Japan role out big names from their past to commentate on their major title bouts (or at least they did pre-Covid) - this is where Flair fits in, he creates the biggest connection to the WCW/NWA history that AEW very clearly want to make theirs. You can have all of the Jakes, Stings, Tullys and Arns that you want but there is no name more synonymous with old school wrestling than Ric Flair.
I'd have him present the belt to the Champion after World title bouts, commentate, or at least be rolled out ringside, for those matches and maybe be a talking head on some segments that breakdown how the AEW World Champion compares to Champions past or how Omega vs Cage compares to Flair against Steamboat (as an example).
There's room for him in AEW specifically because they embrace wrestling history and associating him specifically with the World Title does a lot for that title (in my opinion at least).