Not necessarily the jab. Any viral exposure can do it. Usually respiratory infections, sometimes intestinal, sometimes vaccines, etc. I had an upper respiratory infection in 1973, came down with GBS. I never fully recovered but got back about 85%. Back then they didn’t do anything beyond some prednisone.
My sister had GB years ago and pretty much recovered. Then last year the husband of a friend got it.
It was the jab because she mentioned it. LOL
USUALLY the cause of GB is an acute viral infection, right? COVID develops exceptionally high viral loads, often even when symptoms are mild to none. So, while the risk of GB from a vaccine is very low, I can imagine that a vaccine-tamped-down-to-asymptomatic COVID case could induce GB that seemed to come from “nowhere”.