Thanks for the answers, it's working now. I exported as a signed APK. But there was also something wrong with my Admob Account. On the Admob Dashboard it showed the warning that I didn't add my address and Admob won't show ads (and the consent pop-up apparently) until I add my address.
Did you add the consent pop-up to your project or is it supposed to display automatically,as part of the plugin?
It should display automatically if you use the MobileAdvert plugin and configure it in your Admob Account because AFAIK the Consent Dialog is not coming from Construct but from Admob.