Windows has had a concept of "Shell Namespaces" ¹ ² ³ for about 20 years now that allows developers to add support for interacting with things in the File Explorer that have tree structures but that do not need to part of the OS's official filesystem.
For example, you could make one for FTP, for Zip and other archive types, etc.
I can't seem to find by Googling what the MacOS equivalent is, or if it simply lacks an equivalent altogether.