I replaced my Fire TV with a mini PC, and now my TV does things Amazon never intended

My Amazon Fire TV has lived under my TV since 2015, and for most of that time it did exactly what I asked. It's the square second-generation box from before the Cube, and it still sideloads anything I throw at it. But Amazon's guaranteed updates for it ended in 2021; it never got the new interface, and apps have been dropping support for it ever since.