Detailed explanation of Object creation and memory allocation in OOPs Advanced

Confusion in object creation & memory allocation in OOPs, Clearly explained in this video C#.Net core
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[bhargavikommineni]

very informative video in simple words, thanks!!!!

[valorantfever]

what happens in runtime polymorphism, when we create child class instance and reference as parent class, for example ->
Parent P = new Derived(); , in such case does the dotnet assign memory to both parent and child class or anything else?