Even just not using your car to do journeys of less than a couple of miles.
I don't exercise at all, really. I just walk everywhere, to do my shopping, and for fun. I don't run or jog or lift weights. I cook food from fresh as much as I can, avoid too much meat, and I don't have a car. I have a healthy weight and a small (usually) waistline.
Like a lot of us I do occasionally still have back problems from too much sitting (as I enter middle age) but literally just a couple of weekends of daily, hilly walks will put things back in order for some time.
It's also an effective mild antidepressant and sleep regulator.
If you want a life choice that will help you lose weight: move somewhere you can function as much as possible without a car.
Most people don't have the freedom to make this choice, but the fact that the people who do genuinely have the freedom and who can see their whole family is overweight never even consider it, often surprises me.
(We should be developing societies that can function this way at a larger scale, not just developing on-demand delivery services.)