If Widget Component User Interface`s Geometry Mode is set to Cylinder, the button of binded UserWidget can`t be clicked.

The script, mate. See my answer below. Seems to work just fine in 4.27 (and it 100% worked in 4.25):

Image from Gyazo

If you still cannot get it to work, double check the widget hierarchy I mentioned. Your arrows do not answer that at all. Perhaps something got accidently blocked - every native widget has its own granular setting for this: