Forgive this post as I know you're not the "Yammer" community, but they've glossed past my original post so I'm here to ask if anyone else has had this issue too. In summary,
The "All Company" community cannot be used with the Yammer connector in Teams
It cannot be used with the Yammer web part in SharePoint
I cannot access the community settings as neither a Network Admin or a Global Admin
I have a ticket with Microsoft but they've has gone dark on the matter in the last 24 hours
My growing frustration is that I've reached out in every corner of the internet that I can think of but I've gotten zero responses that either acknowledge this as a bug or a known limitation of the AC community.
So that's why I've reached out here so see if any of you have experience setting up the "All Company" Yammer group. Or at the bare minimum - some confirmation that I'm not the only one with this issue.