A lot of truth here. When my BMI was high, just the reduction of calories and the daily exercise (walking) was enough to lose weight.

I've also had RMR (resting metabolism rate) tests to get some idea of base metabolism and DXA (differential X-ray) scans to identify lean vs adipose tissues.[1]

The goal for me was to find a 'budget' of how many calories a week I could eat based on my level of exercise and maintain my weight. That involves spending a lot time tracking what you eat (and for me breaking up calories by fat, carbs, and protein). All to just to data analysis and to create a data driven mental model of what I could eat and how it would affect the aggregation of fat.

[1] Not sure how widely available they are but I've used Bodyspec for both (https://www.bodyspec.com/)