The portal setup is failing on my instance

FRE

I am blocked in the 3rd step on the Portal Configuration

After entering Portal Details to configure a Portal it takes a long time for the Portal configuration page to come back

The screen then is in readonly mode on the Portal side, no configured Portal is visible and buttons (beside the continue button) are blocked (see also in the attached screenshot file)

Can I just reset the CRM preview instance and try again?