mod installed

• Client side : JEI, FTB Library, Architectury
• Server side : JEI

In this case, the players can enable cheat mode in the server (even without any permission) and use give mode to get any items they want.

Thanks for the report!
I have added some new server-side configs to enable or disable cheat mode in JEI, that will allow server owners to control this behavior. 574bb25

That's probably because they have operator permissions (/op)