When I run git clean --dry-run the results are a bit like:
git clean --dry-run
Would remove an_untracked_file Would remove an_untracked_file_2 Would not remove some
By default, git clean doesn't remove folders. It's telling you that it sees an untracked folder, but it won't remove it. Give it the -d flag to instruct it to remove directories as well, as in git clean -d -n
git clean
-d
git clean -d -n