I'm trying to assign the only layout created there: Course Page Layout.
Although it's assigned, when I load any Course, for example the link below, the layout is not applied. hidden link
Also, could you clarify, in this case, the difference between a Layout and Content Template?
I just switched to the default 2020 theme and I can see the Layout you created for Course is applied:
=> hidden link
It looks like your theme is not using the standard the_content() function to display the content.
However - I would like to inform you that Layouts plugin is in maintenance mode only, having said that there will not be any new features added. Why dont you try to use the Toolset blocks to build your single page for your post type?