As a freelancer, this is a terrible way to filter it IMO. A lot of people come to me expecting a website to be built in, say, Ruby. I ask them why not JavaScript, and they'll tell me that JavaScript has some licensing issues with Oracle. Or some pick Cordova because it's easier to maintain one code base (it's not).
It's hard enough for someone who does it professionally for years to know why they should pick Flutter over Native, or Vue over React. Most people probably can't afford the best stack anyway. Let the freelancer decide what's best to build the product in.
That would be part of the interview process - figuring whether their language of choice is replaceable. Most languages are learnable; every project I've joined was built in a language I had 0 experience in, but it's not hard to just hack in fixes or even rebuild modules completely.
Outsourced work tends to be hacky and unmaintainable for the most part. Sometimes it's built cheap, with no architecture whatsoever or designed for a very specific situation. Even worse, it could be overengineered.
It's hard enough for someone who does it professionally for years to know why they should pick Flutter over Native, or Vue over React. Most people probably can't afford the best stack anyway. Let the freelancer decide what's best to build the product in.