I imagine that this is not good enough for what you are after but it is a real world example of what I did when I needed something vaguely similar.
This is perhaps best described as a "bodgy work around" that was "good enough" for my purposes. Not likely to be suitable professionally and other FreeCad-ers may laugh and think it idiotic, but this is what I did and it served my purposes.
I just made a "block" diagram style of human from solid "cubes" in part work bench. I then "positioned" and "rotated" the cuboids as appropriate to simulate an approximation of a human of a specific size in various positions. It actually worked quite well, for the limited needs of my project.
My usage scenario.
I designed a top bunk bed with cupboards and draws underneath rather than a lower bunk. I wanted to show it to my wife, for her approval, then make the bed myself, for one of my kids. My wife liked the 3d model. I coloured it white and pink and my daughter decided she definitely wanted it, now please, so long as it had a picture of a fairy as well!
How high is that bunk? Is it up to my shoulders or closer to belly button height? Can I reach a toy or something sitting on the far side of the bed?
So I measured her, and made a block humanoid model to see. All parts made from solid "cube" (OK technically a rectangular-cuboid or whatever
Hands just a cube, arms one each cuboid for lower and one each for upper arms (actually my cuboid wife had only one arm and one leg! (which was all I needed for this purpose), main body section one cuboid, cube for a head, legs were just one cuboid (i.e. no knees) as my "model wife" did not need to bend her legs in this case, then a cuboid for a foot.
Then I just "placed"
, and "rotated"
the various cuboids to simulate different positions/posture scenarios.
I was then able to calculate that she would
1) be able to reach up to about "X"mm across the bed standing with flat feet on the ground,
2) be able to reach about "X+Y" when on "tippy toes"
3) need a stool of "so many" mm high to reach the far side of the top bunk.
She could also then visually get an idea of the scale of the bed relative to a human, which she had previously been struggling with when just looking at the plain model.
I should also point out that my real wife is far more attractive and would make a far better model than my "model wife"!