It’s so frustrating having a unexplained symptoms and no answers, isn’t it? I’m so sorry you’re having to go through all of this. At least you can be fairly certain that your symptoms aren’t related to the Guillain-Barré syndrome. It progresses rather quickly once the symptoms begin.
https://www.mayoclinic.org/diseases-conditions/guillain-barre-syndrome/symptoms-causes/syc-20362793
The reason the administrator if the vaccine asked if you’d had GB is that occasionally the Covid vaccine or any vaccine can trigger an immune response in people who had a preexisting neurological diagnosis. I had this happen and my symptoms disappeared in 2 weeks without treatment.

Being active in the discussions with our neuropathy group I hope it gives you some solace to know you’re not alone. Good luck with your doctor’s appointment coming up. I hope your next doctor isn’t rude to you! There’s no reason to tolerate that! Did you let them know why you won’t be returning?