Here is a masterclass video series by Mihnea Stoica, covering the current state of KineFX Ragdoll tools in Houdini 20.5. Mihnea will go over the core concepts of ragdoll, what it is (physically-accurate animation you get 'for free') and how to set it up using the ragdoll solver, skeleton, collision geo, skin, configure joint limits and bone deform. After that, Mihnea will explain the basic building blocks required for an APEX rig. You can download the free little bot file to follow along. The little bot rig is created by Mihnea Stoica and Henry Dean.
Full video series and project file download here: https://www.sidefx.com/tutorials/kinefx-ragdoll-masterclass/