Hi Wouter,
You could create JavaScript action. Using some code to detect, many ways are described here.
https://stackoverflow.com/questions/8068052/phonegap-detect-if-running-on-desktop-browser
Or play with Mobile device widget to see if you get de right info to make decission.
https://appstore.home.mendix.com/link/app/65139/
And you can also do based on CSS. As you index file for Hyrbid apps can have different CSS files.
https://docs.mendix.com/refguide/customizing-hybrid-mobile-apps
Cheers, Andries
Is the same widget used in this collection, btw @Andries? https://appstore.home.mendix.com/link/app/112063/