As written, it applies to the "music, sounds, text or information that you make available or create whilst using the Service" and gives Flat a "worldwide, nonexclusive,
royalty-free and perpetual licence to use, copy, reproduce, distribute, adapt, reformat, modify, publish, translate, licence, sub-licence, and exploit the User Content
anywhere and in any form." [1]
I can see why artists might be a little concerned about this.
We will update them in next few days / weeks to be more precise about private and non-shared content. This actually more apply to public content (e.g. you can see on "popular" pages).
I can see why artists might be a little concerned about this.
[1] https://flat.io/legal/individual-terms-of-service.pdf