In 2020, The World Health Organisation started working on a COVID-19 app for Nigeria, built with Flutter. I've been actively interested in Flutter since 2017, but for some reason never saw this in any of the Flutter news.

First commit was March 17th 2020, which is 13 days before the first Nigeria lockdown. As a mild tangent, this was 6 days before the first UK lockdown, 2 days before the first USA lockdown and 4 days after the Albania lockdown (the first lockdown in the world).

https://github.com/WorldHealthOrganization/app

It's also a monorepo, which seem quite popular in the Flutter community where Dart is used on the backend.