How to set “power button” to turn screen off?

I set option in “Power Settings” to turn off monitor on press of "power button".

Screen turns off, then immediately gets back on.

Also, dimming screen only works in GameMode, setting brightness or "dim after x min" in DesktopMode does nothing.

I tested setting Power Profile for activity, running app in Activity, but I saw no effect after timeouts or hitting the button.