and the hello>index.php file just displayes hello world
“For example, if the controller class is PostController, the directory would be @app/views/post; if it is PostCommentController, the directory would be @app/views/post-comment”
https://www.yiiframework.com/doc/guide/2.0/en/structure-views#organizing-views
“By default, controller IDs should contain these characters only: English letters in lower case, digits, underscores, hyphens, and forward slashes”
https://www.yiiframework.com/doc/guide/2.0/en/structure-controllers#controller-ids
From your screenshot,
I think your views folder is typo,
All the letters should be lowercase, such as
backend/views/hello/index.php
still get 404 not found
