In this video tutorial, you will know how to change your Facebook friend request to a followers button, so people can follow you instead of sending you a friend request.
you cannot just disable “Add friend” option but you can limit who can send you friend requests.
To do that, go to facebook settings>>privacy settings>> How People Find and Contact You. Change Who can send you friend requests to “friends of friends”.
Then to enable followers, you need to go to “Public Posts” in settings and change your settings in “Who Can Follow Me” and make it “Public”.
piece and having a custom username