Automatically switch your Mac between light and dark modes based on the ambient light sensor.
I've never been a fan of the built-in "Auto" mode on macOS because it's based on time of day and it will not switch the Mac to Dark Mode while I'm actively using it (which is a problem, since I'm pretty much always using my Mac).
The solution for that is DarkModeBuddy. It's a tiny app that keeps running in the background and reads the ambient light sensor on your Mac (the same one it uses to adjust the brightness of your screen). When the ambient light level falls below the configured value, DarkModeBuddy automatically switches the Mac into Dark Mode. When the ambient light level rises above the configured value, it goes back into Light mode. This does not happen instantaneously: in order to prevent flickering, the change in ambient light level must persist for a certain amount of time, which can also be configured in the app's settings.
DarkModeBuddy is open-source, check out the project on Github if you wish to contribute to its development: https://github.com/insidegui/DarkModeBuddy