I don’t have schizophrenia but am severely mentally ill and am reckoned to have experienced psychosis. I have always been very sedentary . When I was younger I was described as poorly coordinated(probable dyspraxia though I think it was called clumsy child syndrome way back when. It was hardly on the radar re diagnosis). I was invariably the last to be picked for a team sport. I sucked at gymnastics. The only thing I was ok at was swimming,though a slowish swimmer. What put me off exercise/sport was the social rejection children who are bad at sports are subjected to by their peers. Then there is the issue with fitness plans- they all seem to require coordination/flow and speed of movement that I don’t have.
The most I’ll do is a spot of walking but not enough to make a difference. If I walk far I can have a tendency for one of my ankles to give way.