New Custom Post Type is not working

-rw-r--r-- 1 user members 842 3月 8 18:21 single-about.php
-rw-r--r-- 1 user members 842 3月 8 18:36 single-course.php

I already have an existing custom post type “about”. It’s loaded using single-about.php
I added new custom post type “course” and copied single-about.php content to single-course.php but the new post under “course” custom post type cannot be viewed.
And there’s also no sign that single-course.php is used.

The solution was to flush rewrite, you can do this by going to Settings > Permalinks and just hit Save Changes and everything works as expected after that.