honestly, I punched way above my weight class with the use of a certain shader in my game, but it kinda worked out, so here I am promoting to use of stuff you don't understand :-)
but honestly, you could just start by pixelating the game (for example: use your players camera to target a render texture with a set resolution and then record a plane with that texture with the actual MainCamera) also Unity's post-processing effects might help in terms of color grading, or even stuff like chromatic abberation, slight lense distortion, grain or a little bloom - essentially recreating the look of an old tv. that's all possible without ever touching any shader file ;-)