IMHO you need to understand the following:
1) understand the models used in MVC...
https://deviq.com/terms/kinds-of-models
2) understand how to use a viewmodel
https://www.dotnettricks.com/learn/mvc/understanding-viewmodel-in-aspnet-mvc
3) understand SoC and MVC
https://en.wikipedia.org/wiki/Separation_of_concerns
https://www.c-sharpcorner.com/UploadFile/56fb14/understanding-separation-of-concern-and-Asp-Net-mvc/
https://learn.microsoft.com/en-us/dotnet/architecture/modern-web-apps-azure/architectural-principles
4) understand clean coding and dependency injection
https://learn.microsoft.com/en-us/archive/msdn-magazine/2016/may/asp-net-writing-clean-code-in-asp-net-core-with-dependency-injection
5) understand to keep the controller thin, which is being talked about in one of the last topics in the link about Understanding Models.
https://learn.microsoft.com/en-us/aspnet/mvc/overview/older-versions-1/overview/understanding-models-views-and-controllers-cs
You should understand the principles of using MVC, becuase the MVC pipeline is being used in a Razor page project the Visual Studio project architecture is the same as a MVC project.
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