My inexpert understanding is that mRNA vaccines such as this one are unlikely to have an impact on many autoimmune cases. In many, perhaps most, others, it appears from my reading to be likely that the generated interferons are not adding anything to the likelihood of developing an autoimmune condition that wouldn't eventually already happen. (It might be the nudge over the cliff, but so might have the next common cold you catch.) But it should be tested to understand, regardless.
People experiencing long term symptoms? I can believe that, my tinnitus after covid-19 is still there, even if I don't notice it as much.
Actual viral infection? I really doubt that, thoug perhaps it could hide like the herpes virus.
At the moment it's all quite nebulous, with a lot of anecdote and not enough data. But there are some studies starting up that might start to untangle what's going on.
I don't know how many people with conditions take immunosuppression medication. I take it for arthritis and alopecia and have come across many people on similar meds for diabetes or other things. But that could be a form of confirmation bias