Four months isn’t long enough to judge anything.
It might be fair to start getting worried if there’s no real improvement whatsoever after 6-7 months. But even then, if you come back here and ask the question again we’ll probably say “give it until the 12 months, then start taking action.”
Transplants often seem to grow in a couple of waves of improvement. One at maybe 5-6 months, another at 9-12 months, and another at about a year and a half. We could debate the specific timeframes that are most common but you get the idea.
Diffuse thinning is a b*tch to transplant in general too. I hope your doctor explained that the number of hairs lost from the trauma of the HT might seriously limit the gains from the whole procedure. If this happens, you’re benefiting from swapping dying hairs for healthier DHT-resistant ones, but there’s not much cosmetic benefit because you were close to “breaking even” on the end result.