Hi Garion,
The widget you’ve linked to has community support, meaning there is no guarantee (even if it would work now) that future Mendix versions will support it.
Any reason why the (platform supported) official mendix feedback widget isn’t an option?
Based on the comments that widget seems to be broken.
Thinking out of the box, a floating action button might be a good alternative.
https://appstore.home.mendix.com/link/app/67293/