As reported by @Papercut in [[ https://developer.blender.org/T78217 | T78217 ]] paw rig type appears to have limitations on the unguligrades rear limbs.
There is a [[ https://developer.blender.org/D8154 | patch ]] submitted by @Mets that solves the issue on the lower part of the limb by replicating the front limb setup. This has some counter indication though:
• the ik is now ending before the knee.
• adding a shoulder-like bone corresponding to human thigh to extend the ik will not extend the b-bone and tweak setup. Tweaks are often used to simulate muscles and fix deformation issues and in this kind of setup the part with more muscle mass will not be tweakable at all.