I can now confirm that the issue lies firectly in third party domains.
For tests I changed to the myshopify.com domain, edited links in the catalog to match and applied with that. I was approved.
Naturally it does not solve the issue for me, it’s not as if I could stay on the myshopify.com domain forever, so I will start testing whether I can somehow transition to my domain without the whole mess of unlinking. I will let you know how it goes. What a mess this is…