Mobs would not move and would have a seizure, sometimes the mob spawning breaks and would spawn so many mobs in one chunk. I don't think this has happened in 1.16.5 cause I couldn't replicate it. I tested this on a superflat world and overworld and there is a little difference, also arrows are glitched and fireworks are choppy and laggy. I teleported to about 50M blocks away. Mob spawning might get worse when you go even further. If you goto the 16 bit integer limit the mob spawning becomes worse and your game will lag.