You must not do a lot of C# code reviews? This syntax is used in every codebase. In fact if you don't use it Visual Studio will underline it as "code can be simplified" suggestion.
You've never seen something like this?
MyEvent?.Invoke(sender, arg);
I work almost exclusively in C#, and I do a lot of reviews. I'm familiar with the syntax, and I use it. It's the assignment version that I'm talking about here.