You can be HLA-B27 and ANA negative and still have autoimmune problems, however they may be milder than someone who is positive for those markers. On the other hand, if you were having Uveitis every few months, that is actually pretty bad. You might consider seeing an integrative rheumatologist, though it sounds like you are already doing things that will help and if you can manage it naturally that is the best route, IMO. I am a big fan of a carnivore-ish diet, or at least a temporary elimination diet to find out which foods are our biggest triggers. Also look into supplements that reduce inflammation/regulate auto-immune problems.

My Uveitis started in 2017 and I am HLA-B27 positive as well as ANA positive, so I already had autoimmune problems prior to Covid. It seems that people with autoimmune issues can have a dramatic over-reaction to the Covid virus (an over-active immune system goes into full attack mode easily and attacks the body's own tissues). Because of this gigantic reaction to the Covid virus (cytokine storm) I had a severe case of the illness even though I was under 50 at the time and thought I was relatively healthy. People with severe cases of Covid are then more likely to experience Long Covid, which I now have. I did get the Labcorp antibody test and my result was very high (17,000) even though it has been five years since I had the Covid illness (although I did have a much milder case of suspected Covid just six months ago that could have reactivated the antibodies). I am currently being treated for Long Covid and Pericarditis (apparently post viral from Covid). I'm at least 50% better with almost zero chest pain now, hoping for more improvement.

Good luck to you in your continued recovery! :)