FYI: the flow connector you have selected for your Flow is not correct there is a specific one for Power Pages (the one your screen shot shows is for Microsoft Forms - a completely different product).
One scenario (may not be your scenario) where you can get the blank window when trying to create a Flow is that your user is not licenced for Flow. There is a direct url for Flow (that I can't find at the moment) and if you use it it will tell you if it is a licencing issue.