The toggle is in your profile settings. It does not appear to be implemented in the Android app yet, nor are there any options under the “App Configuration” tab yet. The app is still pretty new so there will probably be some growth period while it is flushed out.
The Chrome app still works and currently supports the HTML5 push notifications as well as most of the features of the app (aside from location and battery level reporting, which was just added in the past few days). Personally I’ve found the HTML5 push notifications to be very unreliable and have had a lot more success with Telegram