morning,

Looking for any information about scaling properly the bones & mesh

I have different races that uses the same mesh and animation.
the skeleton structure would be similar but the placement would be way different.

I was thinking of having my mesh, skeleton and animation for human.
once I do the animation, everything would be the same as the human, then modify the mesh placement and scale.

Just looking if someone else has an idea, or if this is the better and more suitable for scaling way ?

The only other way i could see is to manually create the mesh assets for all type of races, but that would make scaling races way harder, and increase the work by [n] folds

Not sure if I understand you correctly, but one idea is to have different character models object/mesh/skeletons, all in the same scale.
And then scale them in game, skel.updateMatrix(here enter scaled matrix).

Another option is to allow having different sized/scaled object meshes.
But when using the same animations, then scale AnimSkelBone.pos for the first BONE_SPINE, before calling skel.updateMatrix

Great, yes the skel.updateMatrix() is probably the best way to go.

the bones would need to have the matrix set one by one, so it is a bit of work, but i can probably build a quick editor to work some magic