In file paths, how are forward slashes $(/)$ and backslashes $()$ used differently across operating systems?

Question $72$ options:

Backslashes $()$ are not used in any modern operating systems.

Forward slashes $(/)$ are used in Windows, while backslashes $()$ are used in macOS and Linux.

Forward slashes $(/)$ are used in macOS and Linux, while backslashes $()$ are used in Windows.

Forward slashes $(/)$ and backslashes $()$ are interchangeable in all operating systems.