I think you created the new page in a wrong place. you should click the Button-->Events-->more-->Action-->Create Object, here in the page area you can then create a new page. and you can see the “Pre-fill page contents based on the Course entity”
I'm also new to mendix, maybe it's the version that was mentioned above which caused the problem. Have a try anyway. :D
Ok Here you go>>
You need to go Button-->Events-->more-->Action-->Create Object
Action : create Object
Entity: Course
Page: Course_newEdit
That's it..you will get rid of error
You may not be able to find the checkbox because of the Modeler version you are using. In that learning path it suggests you use an older version of the modeler in order to keep images/descriptions consistent with the tutorial content.
This could also be leading to your other issues, but I'm not 100% sure. I had issues similar this that I had to find workarounds for when doing the introductory learning path until I switched modeler versions for consistency.
Hmmm...where did it suggest to use the older version? When I went through the intro it stated "Go to the App Store, download the latest version of the Desktop Modeler, and install it on your computer" (https://gettingstarted.mendixcloud.com/link/module/78/lecture/661).
In building this app I am actually using the web modeler which appears to be version 2.0.146.
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