S2member secure file upload

I want to upload files to the protected directory via Wordpress, not FTP. While searching for a solution I came across the following plugin:

This is pretty much what I want, but it’s too old. What would be the best way to customize it, so you can upload files inside the Gutenberg-Editor?
(Maybe its also possible to extend it, so you can choose a subdirectory by custom capabilities?)

Thanks for your help!