Hi Gennaro and welcome! 🙂
There are multiple ways to achieve motion blur on a Spine character at runtime.
As Pharan wrote on the thread above, any shader that writes to the z-buffer will also work in terms of creating motion blur in post processing effects. There are multiple shaders provided with the Spine-Unity runtime that provide a z-write option or variant. Note however, that the typical motion blur post processing effect might not be what you need, as it is most likely too subtile.
The recommended way to apply controllable motion blur to a Spine character is via the Skeleton Ghost example script that is included in the runtime. You can customize the ghosting effect in terms of color, blend mode and timing. See this video to see it in action:
Spine Unity Ghosting - YouTube
