While these features don't require any special settings to be enabled on the user's end, developers will have to build support it into their web apps and pages in order for them to be available, so functionality may differ between web pages and apps.
Keep in mind that Chrome's new dark mode looks pretty much the same as Incognito Mode, minus the warning that "you've gone incognito".
With the release of Chrome 73 on Tuesday, the browser now natively supports the dark mode long offered in macOS Mojave. If they do so often for the same web page, Chrome will eventually disable Data Saver for that page automatically. Aside from bug fixes and performance improvements, it brings Data Saver support for HTTPS pages on Android, new "Enhanced spell check" and "Safe browsing extended reporting" features, as well as support for media keys among others.
Chrome 73 also consolidates all options related to Google's sync feature under the new "Sync and Google services" section that was added to the settings menu with Chrome 72 (these changes are still being rolled out following the update, so may not be immediately present for all users).
When a phone has a particular problem loading a web page, the Lite version is shown instead, and Chrome displays a notification in the URL bar to let users know. Some users are able to inadvertently access dark mode so there is at least some information to be had about it but dark mode simply isn't ready yet for the overwhelming majority of testers.
The stable Chrome 73 update is now rolling out on all compatible platforms and will soon reach users across the globe over the course of the next few weeks. Additionally, automatic picture-in-picture mode optimisation for video in PWAs and the addition of a "Skip Ad" button in Picture-in-Picture window are among the new features that have entered testing with Chrome 73's arrival. The novelties of this latest release can be found in the downloads, in the shortcuts for the Omnibar as well as in the Data Saver function, which now also works on HTTPS pages.