I have a Raspberry Pi 4 with the official 7" touchscreen with the latest Raspberry Pi OS installed. In the GUI, I've turned on Screen Blanking. It does exactly what I want -- the screen's backlight turns off and the screen is pitch black. The default time for this is 10 minutes.
I've gone searching the interwebs to change this timing. Though I come up with scads of proposed solutions, I have had no success yet. I want to shorten the screen blanking time to one minute.
Note: I've tried the xscreensaver route, but it doesn't turn off the backlight.