The Nintendo Switch Online app has been available for over a year now, but a drastic increase to its functions upon the recent release of the Nintendo Switch Online paid subscription service caused a surge in installs, bringing it to five million total downloads. That's 25% of total Nintendo Switch owners.
Sensor Tower reports that the release of the Nintendo Switch Online service resulted in a 76% increase to installs during launch week, with 70,000 installs the week of September 10 and 123,000 the week of September 17. The United States accounted for approximately 51,000 of launch week downloads, while Japan accounted for 23,000.
For comparison, the Nintendo Switch Online app saw 240,000 installs in the entire month of July.
The Nintendo Switch Online app allows subscribers access to voice chat and other services for select games such as Splatoon 2, Mario Kart 8 Deluxe, and Mario Tennis Aces. However, installation numbers do not necessarily reflect subscriber numbers, as a subscriber does not have to have the app installed, and the app is installable (if not usable) even without a subscription.