This suggestion by Teresa @hopeful33250 makes a ton of sense to me. The symptoms as you describe them sound so diverse and kind of random, and being in your twenties and formerly healthy prior to your surgery last April, it really does sound like you might have "caught" something very bad. One thing you mentioned is having been diagnosed with sensory polyneuropathy. Who diagnosed that and what tests (if any) were done to arrive at that conclusion? Even if you have developed neuropathy, that would not begin to explain all else that is going on. You have mentioned covid (and I recall Jennifer @jenniferhunter suggesting that back in August as well). I am wondering if an infectious disease doctor would be of service to you in figuring this out? (I know, you have already seen practically every doctor known to man, but really, this might be the right direction to steer toward).
Oh my goodness, I feel so much compassion for you in this! Try to remain calm and perhaps reassess the direction you have been pursuing, I believe Teresa is on to something. Best to you, Hank