As a counter anecdote, I know many people that only leave their house a few times per week, including for walks. They are definitely more sedentary now.
Anecdotally, around my town the lower number of drivers on the road seems to be causing those who remain to feel like traffic laws don't matter. I can't even count how many times I have seen blatant "it's red but there's no traffic so I'll just go" behaviors, along with ridiculous speeding and lane changing. Doesn't help that the police essentially announced that they won't be looking for crime anymore.
I live in Boston and drive every day still. This is anecdotal - but I've seen the same amount of bad driving as ever (largely around merging, roundabouts, and turn signal usage) but now it's at a significantly higher speed because on I-95 and I-93 you can easily hit 85 mph instead of the customary 45 mph the whole way during rush hour.
I don't have any data, but I imagine that explains the similar serious accident rate.
one possible counterpoint: couples in healthy relationships could still be going out more, whereas those in dysfunctional ones might be fighting more due to more proximity or exascerbated economic hardship
https://www.bbc.com/news/world-us-canada-52416330
As a counter anecdote, I know many people that only leave their house a few times per week, including for walks. They are definitely more sedentary now.