DitherDown URP

You can install the project directly from the package manager using the URL provided, or clone it to your computer and install it through the package manager by browsing to the folder. You can also download ditherdown.zip here, extract it, and install the package the same way.

Your camera must have the Post Processing property set to enabled for the pixelization effect to work properly.

In your URP Asset set your Upscaling Filter to Nearest-Neighbour. Set the Render Scale property to something like 0.3333336; I use the target resolution divided by the screen height to calculate the desired scale, ex. 360/1080 = 0.3333336.

Add a Full Screen Render Pass Feature to your URP Renderer. Set the Pass Material to the DitherDown material. Set the Injection Point to After Rendering Post Processing. Set the DitherTexture, DitherAmount, ColorResolution, and ScreenScale properties accordingly. The ScreenScale should be matched to the Render Scale you set in your URP Asset. 

There's also a VHS effect that works the same way. Add a Full Screen Render Pass Feature to your URP Renderer and set the material to VHSEffect. The Color offset property controls the amount of offset, from -0.01 to 0.01, I find 0.001 to 0.003 to look pretty good.