I am trying to enable EFS on a folder and add some others users to access it too. but the Add button doesn't exist on the place it should be. I want to know what is the reason for that ?
You can add a user/key to a single encrypted file only, not on a entire directory. This depend on how EFS works. So, the "add" button will be present only when editing single file properties.
You can use the following command to add a user to a directory:
cipher ".\YourFolder" /adduser Dom\TestUser /s