I think that at this point of the obesity epidemics, we should entertain the idea that there are non-behavioral factors in play as well. Not just "putting in the work", but a more complex metabolic picture.
As we are talking about smartwatches, let me chime in with my personal, N == 1 observation.
I bought a smartwatch on the day that Russia invaded Ukraine (the timing was an accident, though). So, two years by now. I set up 10 thousand steps to be the goal and since then, I met that goal 98 % of the time, missing only 13 days. I loved walking before, but I stayed home when it was too hot, too cold or too rainy; now I go out anyway, so my daily amount of steps has significantly increased. By how much? Not sure, but 30 per cent at least, possibly up to 40 per cent. My daily average now is just slightly under 13 thousand a day.
Now, there are visible and sometimes measurable improvements to my health:
* lower blood pressure (by some 8/4)
* lower resting heart rate (around 48-49, used to be more like 60),
* better immunity, I am no longer particularly sensitive to wind, rain etc.; I believe that this comes from constant exposure to all sorts of weather when walking outside,
* my knees have improved so much that I feel like being 20 again. I no longer remember which one gave me so much trouble that I almost ended up in surgery in 2017. They are both just fine.
But one parameter hasn't budged even the tiniest bit: my weight oscillates around the same base level. Something inside defends the set point, much like something else defends my body temperature.