I know its simple to fix, just remove it from the server, but i added a mod that disables client-only mods from servers so i dont need to manually remove this mod (and others) everytime i copy an updated version of my modpack into my server's folder.
Even after disabling the mod, it still doesnt work until i manually delete jeimultiblocks.jar
more on that here

Please provide more info than "doesn't work". Is there a crash? Does everything else work but the mod's functionality isn't present? Something else?
Has this been tested with only JEI multiblocks, JEI, and Immersive Engineering? Or are other mods present?
Regardless of the answers to the above questions, please provide a log file from a scenario where things aren't working.

1- Sorry for not being clear, by "not working" i meant that if i click on a multiblock in jei, it just doesnt do anything, it doesnt crash or anything, it just doesnt work until i manually delete jeimultiblocks.jar from my server's mods folder
2- No, i havent tested it with only those 3 mods, my modpack has 200+ mods, but i've had this problem in smaller modpacks 1-2 years ago
3- client log: 2024-01-21-3.log
server log: 2024-01-21-3.log

Thank you for the logs. Looking over the client logs, I see that JEI Multiblocks has loaded and is not reporting any issues. Though there are other mods with unhandled exceptions, maybe one of them is doing something weird?

In the server log, looking at the list of loaded mods starting at line 40, you can see that JEI multiblocks is not being loaded by Forge at all, and a search through the log file shows the mod is not referenced anywhere. So I'm not sure how the mere presence of the mod in the server's mod folder could be causing issues when the server isn't loading the mod's JAR file.

Most likely the issue here is some other combination of mods acting up. If you can isolate it to a game with only this mod, IE, and JEI installed, feel free to post a log of that case. Or if you identify a specific other mod that is causing conflicts (i.e. things work with those 3 mods, but fail with mod X added as a 4th), that might be worth investigating too. But otherwise, I'm going to call this closed.

just to 100% close this, i tested it in single-player and multiplayer with only jei, jeimultiblocks and IE, then i tested again but with "mods optimizer" (to automatically disable jeimultiblocks on the server-side) and yeah... the mod worked fine on all cases, so it really is some weird interaction with some other mod from my modpack :/

plus: i started manually removing jeimultiblocks from my modpack's server to fix the issue, but... the mod just doesnt work anymore, at all (in my modpack)... is there any known incompatibilities with jeimultiblocks?

Other than not working at all on servers on 1.16, there are no incompatibilities that I'm aware of