I wonder if it makes the idiotic Federal gun regulation legislation currently working its way through Congress unconstitutional.
No, it does not. And I expect SCOTUS to uphold red flag laws. They aren't much different from civil forfeiture. There may be some "as applied" cases that establish the details of what it takes to be red flagged, but those cases will simply be an instruction book on how to deprive people of rights without offending the court.