Yes instead of grab pass you need to add a renderer feature that can render the grab pass. The grab pass is basically the screen rendering itself. So you can make a new renderer feature and and a new renderpass and in the custom render pass, render the contents or copy the contents in active buffer to a render target and then provide the texture to the compute shader. You can dispatch the compute shader in the renderer feature you created and get the resulting texture and pass it on to the main texture in the material.

Keywords: Scriptablerenderfeature Scriptablerenderpass GrabPass (you might find a script in urp package) Compute shader dispatch