Who did your reverse shoulder replacement surgery? This is a newer procedure and it is possible your surgeon was not optimally experienced.
I had a reverse shoulder replacement surgery at Mayo (Rochester) in 2023. It was not painful at any time and I now have full function. I consider it a fabulous surgery and am most happy. My surgeon teaches others to do this surgery. At my recent visit, he said the newer protheses are so good that I am unlikely to ever need revision surgery. Good news!!! By the way, I did not do physical therapy but did gentle exercises on my own. I also did not do formal physical therapy for my knee replacements or for my hip. I mainly walked - results are similarly great. No pain and no problems.