Some Mac users have found that a directory called AppleInternal is sitting in the root of their Macintosh HD. The folder itself is empty, but is not removable through the typical means.
/AppleInternal is apparently used by Apple for internal development purposes, and thus likely has no benefit or reason to be installed on an average users Mac. Why it is included on some MacOS installations with new Macs (and apparently some reinstalls too) is a bit of a mystery, since these are not Apple employee computers.
If you attempt to delete /AppleInternal directly by dragging it to the Trash, you will find it’s not possible. Additionally, because /AppleInternal is usually an alias (technically a firmlink, which is sort of like a hard symlink but for APFS).