Folders have metadata such as name, date modified, permissions, etc. Is it possible to fill up a whole drive with only empty folders?
According to to this reddit comment and article, yes.
In case someone in the future sees this and the comment is deleted, here is what it said word-for-word.
According to this article each folder record is 1KB each. So a 500GB disk could only contain 500,000,000 folders at max. The real number would be slighty lower, since their is some additional metadata that needs to be stored.