Hello PK10
The stub-site function you mention is part of what is known as EIGRP IWAN simplification. It is a method of employing the EIGRP stub feature in a DMVPN environment making it simpler to deploy than the conventional way. For more information about it, take a look at the following Cisco documentation:
If you would like to suggest a lesson based on this particular feature, feel free to make your suggestions on the member ideas page below:
There you will see the suggestions made by others as well, and you may find that others have made similar suggestions to yours, and you can add your voice to theirs.
I hope this has been helpful!
Laz