(Best) Named Arguments -- I usually like to stick to syntax which is common among the majority of languages I know (multi-lingual), but this looks pretty useful to me. I might try it.
(Best) Mixed Declaration -- Useful for improving self-documentation in certain cases.
(Best) Nullsafe Operator -- I can't conceptualize where this would be helpful in my code yet, but I'm sure there are plenty of places this could come https://showbox.bio/ in handy.
As a runner up, I am intrigued by the idea of creating an object from an expression, just by using new. It feels familiar, comparable to JS's "everything is really an object" mentality.