How do you write platform-specific code in shared files?

Use conditional compilation with platform symbols (ANDROID, IOS, MACCATALYST, WINDOWS) inside shared code, or split logic into files under Platforms/ that compile only for their target. Conditional compilation is fine for small snippets; partial classes/interfaces are cleaner for larger differences.

string GetPlatformName()
{
#if ANDROID
    return "Android";
#elif IOS
    return "iOS";
#else
    return "Other";
#endif
}