The Ultimate Minecraft Mapping Project (UMCMP for short) is an ambitious project that aims to create mappings for every version of Minecraft that exists, going from oldest to newest.
To use mappings from UMCMP, you must use Fabric's Enigma Swing. From there, open the jar for the version you're looking to deobfucate, and then go to File -> Open Mappings -> Enigma File (legacy).