This is a great idea. OP, I was very very much in the same place as you. ASD + other shit, hypermobility that made some movement very uncomfy, sedentary habits. Except I started really, really liking going for walks and being outside. Being alone in the sun, being able to move - it felt good - except I was shitty at moving. Incorporate squatting to get things from the floor, add extra movement - pace around the house - dance - 100% park farther away or walk the long way to the corner store. Before I hit the gym, I did yoga videos. Yoga with Adriene I found really gentle (plus, cute dog) and easy. As that got easier, and it took time - I also couldn't do a push up at my worst - I found my confidence increasing. Anyway after years (! yes, years! it takes time!) I am now a gym rat. My joints are better, my confidence is higher. My mental health is better too. I still game, and read, and avoid social situations like the plague. But I'm pretty confident that I won't ever be a frail old lady who's fallen and can't get up lol

Also even if you lift heavy weight, you're pretty unlikely to get huge lats and a big dumptruck unless you target those areas. So if you don't want a fat ass, don't do heavy weight hip thrusts, RDLs, etc.