Certainly @ollyollyoxenfree, I'll find the information that you don't seem able to find for yourself.
In the FDA briefing document issued by Moderna (an mRNA vaccine) it was stated (Dec 2020, pg 44) The possibility that the vaccine contributed to the SAE reports of rheumatoid arthritis, peripheral edema/dyspnea with exertion, and autonomic dysfunction cannot be excluded.
The document is here (it's a PDF download, so don't click if you don't want it to download, it's safe): www.fda.gov/media/144434/download
Since then other potential links, particularly with rheumatoid arthritis, have been reported, such as in this article in the lancet that describes the flare up of rheumatoid arthritis in a patient who was in clinical remission: www.thelancet.com/journals/lanrhe/article/PIIS2665-9913(21)00108-9/fulltext
To be clear - the article isn't stating a link, it is suggesting a link and concedes that the flare up may be coincidence. The FDA has considered the link in other briefing documents that you can find yourself - to be clear they have considered the link based on the small amount of evidence available and the known mechanism.
I know what your next objection will be - that there isn't evidence around the long term effect. Yes, due to the short amount of time that has elapsed since the introduction of the vaccines, there isn't long term data, however, as I've detailed before scientists, ie people who aren't just making it up, have suggested there may be a link and there is a small amount of research evidence to back up the possible link.
I'm done now with providing you with articles. You don't need to agree with me. The point still stands that no one, no you and not I and not anybody, knows the long term consequences of injecting people with mRNA.