NOTE: The functionality of saving a site as a template described in this article is supported in SharePoint Online (classic sites only). More information read in Microsoft documentation
How to create a site template:
1.To create a template, you need to go to the course that you want to use as a template -> gear icon -> Site Contents - > Site Settings -> Save site as a template. Then you will be able to use this template to create courses.
2. Create SharePoint Subsite using this template:
3. Create Modern page:
4. Customize it if you want
5. Go to the Site Contents -> Site Pages -> remove the previous Course.aspx page
6. Rename newly created page to Course.aspx -> Make homepage
Make a created template as a default.
How to delete created template:
NOTE: to deactivate templates you must be a site collection administrator
Please, click on the Gear icon -> Site Contents -> Site settings -> Under web designer galleries -> Solutions -> Deactivate the selected template first and then delete it: