Thanks for playing! It's a custom set of render passes that I wrote during the Jam. There's a pixelation effect which renders the base game down to a low resolution and writes that to a render texture. That render texture is then quantized to a given palette so it has refined set of colour to display. And finally that render texture is placed inside a Unity Canvas which a second camera renders out to the screen. That last step is important otherwise you would see bad jittering as a native camera moves across a low resolution representation.
Because of this, it allows you to get away with a lot of cheap assets, mostly which are coloured boxes and cylinders. I appreciate the comment, thank you.