We live rurally, got fields and fields of walks from our doorstep. Y11 DD gets out about 3-4 times a week, walks alone, occasionally meets a friend (once a fortnight or so), but horrified at my idea of her meeting other friends for walks - 1 of her friends isn't allowed out for walks with friends unfortunately. Won't walk with us, won't do any other kind of exercise (we also have a treadmill and spin bike in garage, subscriptions to Peloton and Apple Fitness+), won't do any of the PE/Games lessons set by school.
DSY9, I forced him to do C25k with me over the summer, he did really well, but didn't really keep it up. Got him an Apple Watch at Xmas to motivate him, but he's not restarted. Will walk with us under duress occasionally, DH got him out for a bike ride yesterday. Games online with friends, but doesn't meet anyone for a walk. Bought him a Switch active game last night in desperation, and he seems to quite enjoy it. It's not going to make him an athlete, but gets him slightly out of breath, and at least he's moving more than his thumbs.
DH and I are both really active, so find their apathy particularly frustrating. Neither seem capable of finding any other form of entertainment than a screen. DS who already wears glasses seems to have worsened, taking him to opticians this week.