The description mentions side effects such as GetNextId(), but creating that object doesn't look like it has any side effects, so perhaps not the best example.

As I wrote in another comment, ignored side effects are perhaps the one questionable aspect of it. I usually assume RHS is evaluated first, regardless of what happens on the left - but I'm not sure that mental model was actually correct. But keeping that would mean having to simply do explicit if _when_ there are side effects. So

    if (myObj is not null)
       myObj.Id = GetNextAvailableId(); // Side effect

But for non-side effects

    Settings?.RetryPolicy = new ExponentialBackoffRetryPolicy();

It's obviously hard to know when there are side effects, but that problem already existed. You could trip this up before too e.g.

    var id = GetNextAvailableId();
    if (myObj is not null)
       myObj.Id = id;

Would have tripped you up. But at least it's obvious WHY it would. Something I have long sought in C# is a good way of tracking what is pure and what isn't.