WD Discovery installation unusable on macOS 10.11.6

I just wanted to install WD Discovery 3.7.214 on my old iMac running macOS 10.11.6
After finishing installation all I get is a blue window for WD Discovery (see screenshot). I’m stuck here, can’t do anything more…

What can I do? Suggestions welcome!!

Bildschirmfoto 2020-04-12 um 11.38.38|322x500