Unable to Git-add with force

I get git-status at ~/bin:

# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#       screen/dev/

I run

git add --force screen/dev/

I get the same git-status as before. I add each file in the folder independently, but I get the same git-status.

There is no .git in screen/dev/. The folder seems not to be a sumbodule.

How can you add a folder and its content with force to my git at ~/bin?

From stackoverflow

• Is that a typo on cut paste?

  If not, it should be

  git add --force screen/dev
  

  Masi : Thank you for pointing that out! -- I fixed it in the post.

• You should not need '--force' or '-f' option: see git add:

  -f
--force:

  Allow adding otherwise ignored files.

  In your case, you may not want to add all files, included ignored files under screen/dev directory.

   git add screen/dev
  

  should be enough (without options or ending '/')

  Masi : The same problem occurs also without `/`.

• Try doing:

  git add -A .
  

  Also, if you have a .gitignore file it's also possible that you are unintentionally ignoring something (ie: possibly the files you are trying to add).

  Masi : The same problem occurs also after running your command. I do not have the folder at the .gitignore -files.

• The problem can be solved by renaming the folder and adding the folder with a new name to Git.

  This suggests me that there must be some file manipulating the folder name dev.