It’s a slang shader, so you’ll need to switch your video driver to glcore in settings > driver and then close RetroArch and reopen it. Then, go to the online updater and update slang shaders.
Then, load the core+content, go to the quick menu > shaders > load shader preset. Go to crt > vt220. When it loads up, it’ll populate the passes at the bottom of the shader menu. In each pass, go to the line that says “filter” and press left/right until it says ‘linear’. When they’re all at linear, hit “apply changes”. That’s it.
If you want it to apply every time you load the core, in the same shader menu, go to ‘saving’ > save core preset.