If the patent I applied for was authorized and later expired, what about the patent fee I collected before?

If it is deemed invalid by the Patent Reexamination Board, your patent will be invalid from the beginning, but the civil acts that have been implemented before the invalidation decision takes effect will continue to be valid. If it is obviously unfair, for example, if you receive hundreds of thousands, people put a lot of money into production in the early stage. As a result, people just came up with your patent, which is invalid, and you can ask for an appropriate return.