There are some minor quality-of-life improvements and a reworked design in Nintendo's Switch Online mobile app. The app was launched after the Nintendo Switch. It's designed to work with the console to offer features that aren't available on the Switch.
The most interesting improvement of the 2.0 update is that it offers an easier way to find and share your friend code, which is the primary way of adding friends on Nintendo's online service. You can easily copy the code from the app to the console with a single tap, instead of having to manually copy it from the console. Sharing the code for your friend's console is easier now that you have to type out the 12 digits manually.
There are more minor updates available with the 2.0 update. Nintendo advertises that the app now shows which friends are online, and also lets you change your online status.