Screensaver is no longer activated

Yes, when displaying the graphical interface, the FLAG_KEEP_SCREEN_ON flag is used to prevent the screen from entering screensaver mode. When the screensaver is enabled, the Android system begins to restrict the functionality of apps and network interfaces. This leads to disconnects.
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If you want to see a black screen, you can solve this problem through the graphical interface itself. For example, create a separate layer (page) that is black. In the main page of interface, create a button (screensaver) that will navigate to the black page. On the black page itself, place a large, full-screen black button that will return the interface to the main page. This will create the effect that clicking anywhere on the black page will open the main screen.