Use the Vocoder device set to "Retro" or "Pulse" with a low band count (8 or 12 bands) to achieve that chunky, pixelated vocal sound.
If you want the absolute easiest way to get "that" sound for free, is your best bet for a synth-based approach, while the KeroVee combo is the way to go if you need to process your own live vocals. bitspeek free alternative
It has a "vintage" toggle that emulates early digital processing. Use the Vocoder device set to "Retro" or