Why can't I press the Install button when installing applications from unknown sources?

I'm trying to sideload an application, as seen in the picture below. I have allowed the installation of applications from unknown applied actions in settings, but I can't seem to press the install button. The cancel button works correctly and installing applications via adb install works correctly. What's the problem? EDIT: For those who have this problem, using ChainFire's [C.F. Lumen](https://play.google.com/store/apps/details?id=eu.chainfire.lumen) will correct it because the app uses hardware compositing, and Android doesn't notice a "layer" on top of the current screen.