Mendix support has a solution for the problem.
You need to work offline with the modeler. (Sign out before creating a new project). Now the blank app exists. After creating the project, you can log in again and enable team server for version controll.
It’s still more a workaround than a solution, but it works.
I created a new app in 6.10.3, which does have a Blank starting point. Then, I opened the app in 7.2.0 and was able to convert it in place.
This definitly seems like a support ticket to me;)
Can't you use the completly blank option?