You don't have to exercise so much as get moving.
I'm the best I've been in 37 years, and it's because in August I started forcing myself to just keep walking whenever I went out to have a cigarette. I was in Boston, and would end up ~nowhere and exhausted.
Then started doing random stuff: "might as well walk to Harvard Square instead of the bike path again" "might as well go to a bookstore instead of somewhere random" "I should use the skate park, I don't fit in*, but I miss rollerblading from middle school"
Then my dog died, 2 days later I severely sprained my ankle at the skate park and couldn't walk anywhere substantive for a couple weeks. By the time I'm able to do a sustained 10m+ walk it's winter.
Went to visit California as a not-tech-employee for the first time, so I saw San Luis Obispo and Los Angeles for the first time. And the same habit kicked in, in SLO I ended up hiking for the first time on what I find out later was not a real trail, end up hiking every day that week.
Get to LA and it's nothing like I would have thought. Egalitarian, tons of stuff to do, and Waymo is a godsend. Whenever I get antsy there's somewhere to go and a way to get there.
2 weeks later, I got an apartment in LA, moving away from Northeast for the first time in my life. I could see me just spending another 4 months decaying in Boston until its barely warm enough out to take a 30m walk, and I'm tired of that cycle..
All that to say, I'm fit, I had a great career in high school sports, I played basketball occasionally, but couldn't really get active consistently. Treadmill was never stimulating enough to keep my attention on anything other than being bored. In retrospect, I really wish I heard this old saw ~all of us know and heard it as "moving around" instead of exercise.
(n.b. this was all under active mental health care x medications spanning a decade+. It's not that the mental health care was useless, I don't think I could have done what I did without it. But it couldn't "fix" me on it's lonesome, only enable me to get moving.)
* in retrospect this was wrong, plenty of newbies, and one of the most welcoming social environments I've been in. just people out there all trying to do the same thing and supporting each other.