I recently saw that the cloth brush is now open for people to use, but I don't know how to get it?
Click on the following link to download Blender 2.83 Beta from the official website (It's still experimental).
After downloading, Open blender and go to sculpture tab and you will find the brush in the left menu (T menu).
The cloth brush a feature that is currently in development and therefore not yet included in any release or nightly builds. The differential still needs to be reviewed by other developers before it will be included.