The "Group Files" section is specific to each group. Any files you upload into the files section will only be visible to that group.
If you need multiple groups to be able to access a file, you can upload or embed it into a module then share it with those groups.
Follow these steps:
Step 1. Click on the My Modules tab.
Step 2. Click the title of the module to open it.
Step 3. On the Create Your Module Content box, click on the Media Library icon as shown on the screenshot below.
From here, you can add files by clicking on the Images, Videos, Audios, and Documents tabs, then clicking the + sign to upload a file from your computer.
To give your clients access to the module, you need to make sure that module is added to a course, and that the course is linked to a group. To learn more on how to do these, read the articles below:
How do I add modules to a Course?
How do I share a course with my clients?
Relevant Article:
How can I access all my files inside the media library?
I want to share modules with my clients - how do I give them access?