I was already fairly active before COVID (distance running 4-5 times/week) but actually became even more active after picking skateboarding back up a few months into quarantine. Several of my friends also started exercising more, though the ones that lifted lost some gains but broke through plateaus once they were able to get back in.

Echoing other sentiments here, if exercise is important enough you'll carve out the time for it no matter the circumstance.