npm run dev returns 404 error

[JintaoLiu42]

Hi Sir, your work is extrodinary and so good, I want to test your scean a liitle bit but after I run
npm i
and
npm run dev
And I visit http://localhost:3000/, it returns 404 error, I assume it's a error about route, but there is no error message, could you help me out?
Sincerely thank you!