I mentioned something I am trying out over here in this issue:

SoftwareGuy/ENet-CSharp#41
SoftwareGuy/ENet-CSharp#41 (comment)

I'm just opening an issue to track it here as well as it is specifically Ignorance that I am using to test it with. Quote of comment here for ease of reading:

@SoftwareGuy I was doing some digging around on this as I'm also in need of Mac and hopefully soon PlayStation, XBox, and Switch support. I found this:

https://docs.unity3d.com/Manual/PluginInspector.html

And this:

https://forum.unity.com/threads/how-to-setup-this-windows-player-c-source-code-plugins-for-il2cpp.537269/

Reading through it, it sounds like Unity supports including native C code in your project and it will compile it in the il2cpp build process. It won't work in mono builds or Editor (because of mono).

I'll try it out with enet and if it works, it should make it so enet supports all platforms unity compiles il2cpp with (which I think is all of them).

I'll keep this issue updated with my findings and put in a PR for review if it works on my local.