io.netty... The big known Problem...

Good Morning friendly Nitrado Forum,

I have the following problem (like many others) and I have created my own modpack which works great in single player mode, but not online. + the server is crashing

Because when I connect to the server I get the well-known io.netty error message. I'll try to provide all the necessary information below

Game Version: Forge Vanilla 14.23.5.2768

Newest Crashreport: in Files

Modlist: https://drive.google.com/drive/folders/1ex9rhip61ixewhy7z-qah7zwyhcn03vo?usp=sharing

I tried the following:

• this cmd ipconfig realase new... (yt Tutorial)
• newinstallition of the Servers bzw. this 1.12.2 newest forge version because in the Crashreport it looks like the Versions of the forge mod

The latest logs

A possible solution to the problem, which I have found out, is that I have the latest Forge version installed and an older one on the server, there is now the problem that no new Forge version can be installed and I have no solution at all on the Internet have found
Error in files: