I made a general mobs farm designed by gnembon on the single player and also on a server:

Version 1.15.2 on server: https://streamable.com/y2gd14

Version 1.16.1 on server: https://streamable.com/zwhdty

Version 1.16.1 on single player: https://streamable.com/qd9t1i

Version 1.16.1 on single player (no mod): https://streamable.com/k2cc4n

(i also turn the mob spawning rule off to test on single player, the fluid cause the lag spike)