MPN ID not found or you don't have access to it

I am having trouble linking my Entry App registration to my MPN ID.

I have found several threads on this topic but did not manage to get my issue resolved. Especially this thread looked hopeful: https://learn.microsoft.com/en-us/answers/questions/1805273/mpn-id-not-found-or-you-dont-have-access-to-it

My situation:
I have a personal account ******@jarabot.com which is the owner of my Azure tenant.

I have registered for MPN but my personal account was not allowed as a MPN account so I have created a new account ******@jarabot.onmicrosoft.com which is the owner of our MPN account (jarabot.onmicrosoft.com Microsoft Entra tenant).

Now I need to connect these two and that is where the trouble starts.
When I am in MPN -> Account Settings -> Tenants and want to Associate Microsoft Entra ID I can only login as my @jarabot.onmicrosoft.com user, it does not allow me to log in as @jarabot.com user hence I am not able to link the tenants.
I have tried adding jarabot.onmicrosoft.com user to my Azure tenant as a global admin and vice versa, but that does not help.
Anything else I should try?