I can take screenshots of the screen of my Android TV (Philips device, Android 9) with an external keyboard using the PrintScreen key, and also with a button remapping app. It works just like on an Android phone: a white frame appears on the screen border, it fades away and a PNG file is saved in the Screenshots folder.
But as opposed to phones, on Android TV it only works on the home screen and on the Android menus. But when any app is open or when a standard TV channel is being reproduced, it doesn't work (no white frame, no click sound and no PNG file)
Is this by design or can it be configured to behave like on Android phones?