Why does NA appear in the upper left corner of the phone? How to solve it?

That is the weather forecast. Usually it comes with its own weather forecast. Because the downloaded weather forecast will prompt you to select a region when you install it and start using it. The default version that comes with it is that there is no city. If there is no city, N/A will be displayed on the taskbar. Click the weather forecast widget on the main page of the desktop and set the city.

Some mobile phones also look like this icon when turning off notifications. Just light up the notification icon in the taskbar (the one at the top of the phone that you pull down gently).