I found the answer here: https://docs.microsoft.com/en-us/azure/role-based-access-control/role-assignments-portal#add-a-role-assignment
It was a missing access role.
Thanks for your time and have a nice day :)
Hi James,
thanks for your answer.
I've already checked that and I am 100% sure I'm in the right subscription - that's why I am so confused....
As well as the other user I am Global Administrator, so this should not be an rights issue.
So I just looked into Azure Role Assignments for my user and it says: "No role assignments found for the selected subscription." - maybe thats the issue here ?
@HarshitaSingh-MSFT, thanks for your answer.... but it seems like some of my own app registrations I've provided access to still doesn't show up.
But nevertheless I see more than before...