I will try.

you can try using Mixamo for automatic rigging, from then on you can edit it however you like i also recommend using blender 3.6 LTS, its the most stable version of blender so far

I wanted to make a model out of this model, but when I add a skeleton to it, Blender either crashes or the bones behave like for a person with Down syndrome.

goodness gracious

make this a player model please