How do i make a Compression Artifact post-process like Imperfecter?

I’m pretty new to game dev and working on a VHS-style horror game. I’m trying to find a free post-processing effect to get those retro compression artifacts (like this video “https://www.youtube.com/watch?v=KopGQLysx2Y”).

Everything I’m finding online seems to be paid (like Imperfecter). Does anyone know of any good free alternatives or tutorials on how to achieve this effect?