You need to make a big deal about the food choices, quietly, in private, to your husband. Your son is 11 and stuck at home. He can't eat too much of the wrong thing if you guys stop supplying it. Do not allow your husband to buy junk and then blame the kid for not being active enough. You really can't exercise your way out of a crappy diet.
Start running with him, or make your husband do it. NonetoRun is easy to follow. I'm doing it with my son (slowly) and I have a bad hip and he wears AFOs 8 hours a day.
https://www.nonetorun.com/
Or do jump rope together. That's great exercise. There are some fun videos on YouTube and TikTok. I've been trying to learn but think it may be worse for my hip than the running.
Also, does he have a Switch? Ring Fit also isn't a bad beginner workout, honestly. I prefer the minigames and individual exercises to the story mode, but a child might like either.