I am creating a modpack right now. It included 104 Mods for 1.16.4
The Pack launches just fine and working very nicely.
However, a server including all of this does launch, but throws a lot of errors and when connecting to it,
everyone just can't. And there is always this very helpful error message:
[Netty Epoll Server IO #2/ERROR] [minecraft/NettyPacketEncoder]: java.lang.NullPointerException
Without any mods, the Server launches perfectly and everyone can connect just fine so the server setup might not be the issue.