I found this video very interesting. She is a licensed therapist in the US, so not just a random person having some opinions lol.
Basically to sum it up because the video is long.....BMI was never meant to be used to calculate individual people's weight it was meant to be used for monitoring changes in whole populations. The research does not show that people who are overweight are less healthy than those who are thinner. Traditional "diets" which are restrictive are not really natural and can often lead to disordered eating and weight cycling.
But mainly the things that make the most positive difference to people's health is eating an overall balanced diet and being generally active and doing some exercise.
Warning, she does use some swear words. (If the research part is too much the bit about what to do and how people can start to help themselves starts at roughly 2hrs 10mins.)
"Diets and weight stigma are making you mentally ill"
https://www.youtube.com/watch?v=tWqGulkvCWY&t=5986s