A broad class of possibly non-unique generalized kinetic solutions to hyperbolicparabolic PDEs is introduced. Optimal regularity estimates in time and space for such solutions to nonlocal, and spatially inhomogeneous variants of the porous medium equation are shown in the scale of Sobolev spaces. The optimality of these results is shown by comparison to the non-local Barenblatt solution. The regularity results are used in order to obtain existence of generalized kinetic solutions.