This nugget of the .NET unified type system. And the cause of oh so much misunderstanding.
My way of looking at it is that it isn’t helpful to think of value-types (structs in C# parlance) “as objects”. You can treat them as though they are, but you need to fundamentally change them (box them) in order to do it. Which has lots of uses for sure; but just make sure you understand what you are doing and why. If a value-type truly was an object you wouldn’t have to do this.
It is a bit like saying all people are meat; technically true, but if you start manipulating me like you would beef, don’t expect me to be quite the same afterwards.
Instead, I try to emphasize that everything can be treated as an object.
Oh, and mutable structs are evil, but you already knew that.