Tested in Minecraft 1.21.1
Neo Forge Version 21.1.115
Mekanism Version: 10.7.8
Mekanism Generators 10.7.8
Just Enough Items (JEI): 19.21.0.247
Just Enough Mekanism Multiblcoks: 7.2 but also 7.3 too
EMI (JEI Addon): v1.1.19

Just Enough Mekanism Multiblocks loads into the game, but you can't interact with its tab, can't move the sliders or Interact with anything in the tab when using EMI

Please see this emilyploszaj/emi#692

This mod is targeting to 'JEI' as is name.
Sorry for about that.

Fiexd, it wourld be works. https://legacy.curseforge.com/minecraft/mc-mods/just-enough-mekanism-multiblocks/files/6170220