MagicOnion VS LiteNetLib

If you're in dotnet land, I'd recommend poking magic onion [0] or messagepack. It'll be much nicer to work with once you have a decent pile of message types. Otherwise it's easy to end up in an entity framework like situation where you're constantly serializing and deserializing, generating serializer wrappers, etc. Although any of the cysharp libs are great in dotnet, definitely recommend checking out their back catalogue.

[0] https://github.com/Cysharp/MagicOnion

Having used it on a previous project, I found maintaining the protocol buffers quite tiresome. However, if I wanted to use it again, I'd be inclined to look into the MagicOnion project, which, in its own words:

MagicOnion? https://github.com/Cysharp/MagicOnion

I personally use this LiteNetLib

Been using LiteNetLib for our current project and it is pretty nice

Currently I'm using LiteNetLib (https://github.com/RevenantX/LiteNetLib) and it's working pretty well. There is a little input lag but it's more than acceptable.

Check LiteNetLib. Judging by your requirements simply passing coordinates back and forth between two clients should work. Designate one of the games as host and the other as client, but just pass coordinates would work over LAN. Optimise from there if gameplay isn’t thet smoot by lerping between past and newly received coordinates.

For networking, file IO, and streams in general, there's Korio and for Java; for just networking, there's LiteNetLib for C#; for what looks like data streams in general, there's Okio also for Java; and Tokio for multi-threaded IO in Rust.

I've been a bit "Unity offline", and even more so when it comes to networking solutions, because of my real job :), but LiteNetLib is quite good. There's also a new HLAPI solution called FishNet which seems very interesting.

This might be handy for you :) https://github.com/RevenantX/LiteNetLib

they might be using LiteNetLib as their low level transport.

You definitely want to a low level API (LLAPI) instead, like f.ex. LiteNetLib, ENet, lidgren or similar. I haven't touched anyone of these recently, except the first one a year-ish ago, so I won't say anything about where they stand today.