Hi Sumaira,
1. First of all, I don't recommend adding these Sales-specific settings to other apps.
2. Does "dynamics 365 custom App" refer to OOTB "dynamics 365-custom"?

3. Since you don't have the Sales app, not all Sales options and settings are valid in your environment. There may be only some Sales settings that are valid, and the links of other settings are invalid or you do not have permission to access them.
You can try adding these Sales settings in your sitemap.
First open the sitemap of the Sales app in the trail instance, you could open it through App Designer.

Then open the site map of the model driven app.
Create exactly the same sub area in the site map of the model driven app according to the properties of the sub area of the Sales app.
You need to pay attention to two properties Entity and URL, these two properties determine the object of this area.
