The path separators are constant between OS versions.
On OSX, when you use a NativePath, as well as on Linux, it’s always “/” - that’s commonly called a POSIX path, BTW, as the POSIX standard has defined it that way and is used on both Linux and Unix.
On Windows, you have both “:” (as a driver letter separator) and “”. But Windows may also use paths like this: “\\server\bla\bla”, IIRC.
Beware that a Mac POSIX path may also contain “:” - that’s a normal name character, then. Macs also can use “:” as folder separators, but only with other APIs, eg. when you use AbsolutePath, or when you use classic File manager declares (usually prefixed with FS…). But if you use NativePath, as you should, then don’t worry about this - just assume “/” is the only path separator and accept any other char, including “:”, even the NUL char, as part of the file and folder names.