This video will show you how to enable the system wide dark mode of Android Q without the need to enable battery saving mode this process will require an ADB command to be applied on the phone.
If you don't know how to use ADB commands click the link below and go to the (1:27) mark in the video and watch till (4:17) mark:
• Solved: Photos doesn't have access to...
ADB commands required:
Enable Dark Mode:
adb shell settings put secure ui_night_mode 2
Disable Dark Mode:
adb shell settings put secure ui_night_mode 1