(Not an answer but wanted to attach screenshots to my comment)
As of August the 2nd, the problem still exists on macOS using Safari.
I've tried with Studio Pro 10.12.1 since the pop up states "Don’t have the correct version of Studio Pro installed? Download Studio Pro 10.12.1", and also with version 10.13.0 recently released.
When will this issue be fixed ? Why bother release something on a platform like MacOS and the you cant open a Mendix App on it from the portal ?