It blocks the test generator but not the C4. Why is that? I've tried all the "shortnames". Nothing is blocked :(

(Max. place 1x) !!!

C4 is not a deployable. It's a thrown weapon. Test generator is a deployable / buildable item. 

Given what you're trying to block, I assume you're trying to limit the placed and remote RF triggered C4:

https://codefling.com/plugins/limit-remote-c4

A okay. THX for the Info!

Unfortunately, I thought something like that.

The "C4" was just one example. 

Do you know of a plugin that prohibits certain groups (PVE gamers) from using items? But not influenced by the (PVP gamer)?

Not sure, it is possible to do, one would just check when the item is used if a player has a .use permission, and if not fail the use with an appropriate message.