https://wccftech.com/how-to/how-to-force-enable-dark-mode-on-all-apps-in-android-10/

At this point in time, there are several apps in Android 10 which support Dark Mode or a dark theme. However, there are some which have been in the queue for a long time like WhatsApp and Facebook. If you're a fan of a dark mode on Android, the latest version brings a method through which you can force all apps to add a dark theme. Let's dive in to see some more details on how you can enable dark mode on all apps in Android 10.

The technique is pretty simple and you might already be familiar with it. To enable dark mode on all apps in Android 10, you have to make use of the hidden Developer Options. We have previously covered how you can enable Developer Options on the Google Pixel 4 and OnePlus 7 Pro. For the rest of the devices running Android 10, the process is fairly simple.