I’ve noticed too ... I don’t think it’s the seat
A photo was posted of a round hole in Trump’s jacket, looked like a bullet hole to me. I am sure he wears body armor but even with that, he probably got bruised. And his feet or other parts may be sore. A huge shock to the system a few days ago.
The President went down pretty hard on that stage, and some of the security people slammed him so hard his shoes flew off, so he may well be suffering some bruises and muscle strain. We oldsters take a while to recover sometimes.