Get a list of "Other organizations you belong to" from all users

Couple of keys here.
1-if you can get it for your self (a global admin) then you can get it for everyone, so it must be possible
2 - i matters were the attribute is stored. One of the things i have learned is that AZURE has several DB's of info not a single one like on prem. So connect-azuread is not the same as MS graph or others.
3 - as i understand it, MS Graph is the new hotness, and I would bet that if you explore connecting to your tenent under this method (GUI, powershell, html) you will find the property you want. after you have the place, and attribute, it is a simple matter of looping it to get them for all.

I know this s not a direct answer, but i pray it gives you some hope of a direction.

I have exactly the same question...

Bumping this to see if there's any traction here? This seems like a key thing to be able to do and there's no sign of any way to do it...

This is truly a mystery. Individual users can easily review the "other organizations" but as admin I cannot find this information anywhere! We have been reviewing our own external guest users which made us think of how our users must exist the same way in other tenants. Given that we can see some private information about our external guests i.e. IP address makes me think that admins urgently need this kind of insight into how their users are connecting to other tenants.