I think it heavily depends on the individual. Personally I've gone from nearly sedentary to running ~35 miles per week (and lost ~15 lbs in the process).
I've gone from walking 80minutes/day and doing 16-8 'fasting' to eating comfort foods and barely leaving the house. Principally for me I was able to use getting to work as a motivator to exercise (and everything else fell in to place to some extent); now work is in the bedroom. It's a problem principally of depression/lack of motivation; but one that I was managing prior to lockdown.
Experiences are so varied across the board. It wouldn't surprise me if overall people, like me, were worse off in general health terms.
While it's an amazing progress, make sure not to overdo it. Muscles get used to increased stress quickly, but joints (especially knees) and tendons not so much - and those also heal much slower after a stress-induced injury.
A really good point! I'd run a bit in the past - though not to this extent - and it's amazing the degree to which injury management becomes a part of running. I'm definitely an amateur compared to most people, but I've already learned so much about random human anatomy each time something breaks...
Experiences are so varied across the board. It wouldn't surprise me if overall people, like me, were worse off in general health terms.