1.16 has a bug where certain mobs (which implement the Angerable interface) in mob spawners & other client contexts flood the console with errors (60+ errors per second, which causes drastically large log file sizes and lag). This mod fixes the issue for vanilla mobs (note that non-vanilla mobs which implement Angerable will have to fix this themselves).
This mod is not needed on servers, but nothing bad will happen if it is loaded on one.
CC0-1.0. Fabric mod loader.