For now updates to Google Calendar and Keep are available only in Android versions. The options are different and dark calendar mode only works on devices with the Android Nougat operating system or higher, while Google Keep also allows you to select the option in Lollipop.
The dark mode can be activated in the settings menu of the respective application. In the case of Android Q, the next version of Google's operating system, apps will automatically go into dark mode when the dark theme is selected in the general settings.
Updates for the two applications will gradually be available to Android users over two weeks. In the case of Google Calendar the process began on May 16, while for Google Keep started on the 20th of the same month.
In addition, other Google applications, such as YouTube, Play Games or even the calculator, have been updated to allow the user to opt for the night mode.
The night mode, besides offering an alternative visual aspect, allows to save battery, as Google itself has already confirmed.