Why can’t I see all of my groups in the attach –> group files section in the Outlook desktop client?

I’m trying to attach files from a Team (Group) to an E-Mail via the regular attach file option in the Outlook desktop app, but I can only see a limited number of my groups in the list. i’m wondering where i can find the rest or how I can add groups there so I can select files easily.

I can see all groups in the web application, but I want to use them on the desktop as well.

Any ideas?