Currently playing and JER seems to add not tabs whatsoever to JEI. I even created a world gen.json to config, but nothing.
Playing on 1.20.1 and tried with latest iterations.

Playing on a barely modified version of this modpack: https://www.curseforge.com/minecraft/modpacks/prominence-2-rpg
Which originally ran REI.

I have the same problem

Version of JER? Can you share a log file?

latest.log
JustEnoughResources-Fabric-1.20.1-1.4.0.247
jei-1.20.1-fabric-15.2.0.27

Same here