This app allows you to change the current System's Dark Mode by using a Quick-Settings tile.
To insert the above-mentioned tile in Quick-Settings, open the Quick Settings and manually add the tile in the list of available tiles.
Please note that not all Android versions/devices allow apps to change the System's Dark Mode. In this case the only solution remains to use the Android's System Settings.
This app allows to change the System's Dark Mode by using a Quick-Settings tile.