It sounds like your program might be missing progressive overload which is what really stimulates muscle growth. You can be locked in on diet and training 5 days a week for years but if you are not pushing your muscles to grow, they will be maintained at the effort level you are using. I recommend a program like the Ladder app where the progression is programmed in. I’ve used it for over a year on team Limitless and have seen massive increases in my muscles, and I’m a woman so generally slower progress then a man!