I know in the web player the user can (used to be able to) get to the c# code you’ve written and see all you classes and methods and so on. (unless you obfuscate)
Is this possible on all platforms?
Is there a platform where your code has some privacy?
It’s always possible to decompile .NET libraries and, by extension, pretty much any Unity game. Some platforms are harder to decompile than others, but the only way to keep code “private” is not to share it with anyone.
Note that native libraries are harder to decompile, so if you have a particularly brilliant implementation of a certain algorithm, for example, you could choose to write that as a native plugin in C++ rather than in managed code, but the truth is that it would unlikely be worth the effort.