When creating a new game profile ("Installation") in the launcher for Minecraft Java Edition, you are able to specify a Game Directory where information specific to that profile will be stored.

Relative paths do work in this field - for example, if you create a profile to play on version 1.12.2, and for the profile's game directory you enter

profiles\vanilla-1.12.2

Everything works and the game launches. However, if you investigate the file system in the above folder, you see the directory structure is doubled - example below.

Specifying an absolute path does not experience the same issue, e.g.

C:\Users\user\AppData\Roaming\.minecraft\profiles\vanilla-1.12.2

I think I can best explain this as a directory tree. So, this is what the folder looks like:

• .minecraft
  • profiles
    • vanilla-1.12.2
      • logs
        • ...
      • profiles
        • vanilla-1.12.2
          • resourcepacks
            • ...
          • saves
            • ...
          • realms_persistence.json