Yes, I did that.
OK, you guys are gonna hate me, but I finally got everything to work.
It was several very stuipd problems that actually had not much to do with the actual coding.
But just for completenes, I am going to list them:
It was years since my last server setup (I made that once and ever only migrated it), so I forgot I had to accept the eula.txt.
Which I didnt notice becaus I couldnt find, where the server and by this logs is located, that is run with gradlew runServer. It is under ./run in the main folder of the project
Somehow I had registered the same event twice in the bus, which must have confused the BUS or simply borke it, because it was ingored
After making it only on registration, it was actualy working.
I migrated my server from Minecraft 1.12 to 1.14, and somehow the server starting with forge changed.
I launched the minecraft_server.1.14.4.jar and not the forge-1.14.4-28.0.75.jar
In 1.12 with forge this was enough to get a modded server, but in 1.14 with forge you have to start the server using the forge jar
Now the server is no longer vanilla but a real forge server
and forge is working just perfect includind my mod.
Anyways, sorry for wasting your time, since my actual coding did work from the beginning...
Have a good one and thank you very much for your guys help!