"[DllImport("__Internal")]" - what does the "__Internal" mean?

• Plugins link their code to C# unity using [DllImport()].
• __internal is a keyword used for static linking needed by specific platforms, such as XBox and iOS.
• Other platforms usually use dynamic linking, hence this is not needed.

Please for more info refer to: https://docs.unity3d.com/Manual/NativePlugins.html

Just the minor tip.

If the library being loaded is __Internal, then the main program is searched for method symbols. This happens to be the case on iOS platform.

The plugins on iOS cannot load dynamically. Only statically as @RaxelZ explained.

It is different for OSX, Windows, Android ... those platforms may load plugins dynamically. For iOS, only statically.