qiaoshiyang
Don't say you are stupid! We are all trying to learn here together. 😀
Basically having arm/leg sleeves like this. Those are like the fat layer geo, meaning there's a thickness to it, and simmed like muscles (having material settings like a muscle). This also helped with more extreme forearm/knee bending poses, giving space for the fat solve later on.
I experimented with having another piece on the torso, but ran into similar issues like what you are having with your fat solve. Maybe my collision settings weren't right. But just having these arm/leg sleeves already gave me sufficient space for the fat solve, so I went ahead with this.
Hope that helps!