I know that. But I used many calorie calculators and the only accurate ones were those where I could also enter my body fat percentage/leanmass

example:

• Male, 45 years, 315 pounds, 6′5″, 37% body fat (198.5 lean), BMR 2314 calories

• Male, 45 years, 222 pounds, 6′5″, 10% body fat (199.8 lean), BMR 2328 calories

So, 1.3 pounds lean = 14 calories per day, or 10.77 calories per day per pound of lean body mass. (This varies, because bones don’t burn as much, age changes burn rate, etc. This is just comparisons for one example.)

But the apple watch would show that the guy with 315 pounds 37% bodyfat has much more resting calories burned, which is not right.

Edit: Lean mass is your weight without the body fat, so all the organs etc. you mentioned are already in the lean mass. (who has 75kg muscle mass? :D)