When Google rolled out Android Q beta 3 for the Pixel devices, they included a neat developer option to force the dark mode in any app (though the option was broken in Android Q beta 4). This option is intended as a crude way for developers to test the UX of their app if a dark theme was forced on it, so they can make adjustments to prepare for the stable Android Q release. For users, this new option was an easy way to get a system-wide dark mode in all apps, though it doesn't work very well in every app. It's also an all-or-nothing toggle, which is why XDA Recognized Developer Quinny899 made the new DarQ app. This root app lets you selectively force dark mode to only be enabled in the apps of your choice.
For example, I found DarQ useful for toggling on dark mode in Instagram but keeping it off in Visible. While using the override force dark developer option in Android Q, the Visible app has some nasty UI conflicts that prevent me from seeing some of the UI elements I need to select. With DarQ, I am able to select just Instagram to be forced into dark mode. You can customize which apps on your phone you want to show in dark mode and which you do not.
Another really nice feature in DarQ is automatically turning on the dark mode at night. DarQ can check the time on your phone and turn on the dark mode when it's late, reducing strain on your eyes when you use your phone at night. The Android Q beta currently does not support this feature unless you use Tasker, but other OEMs like Samsung have added support for it in the past. This automatic switch will also work with apps you specifically enable dark mode for, as well as System UI and other supported apps. This app is great for anyone who wants to be able to customize the look and feel of the apps on their device
DarQ requires root in order to run the following shell command: setprop persist.hwui.force_dark true. It also requires an Accessibility Service for its per-app dark mode toggling. Thanks to the latest Magisk update, all Android Q devices, including the Pixel 3 and Pixel 3a series, should be rootable. If you want to download the app, it is available on XDA Labs. Its source code can be found here.