I am using Flutter and have the same concerns. There are many companies that use Flutter, but Google do 99% of the development and don't seem to be using it for any of their own public apps, which is discouraging.
Well, they did a Big Damn Rewrite to use it for Wallet/Pay, and, in the process, dropped a bunch of features and made it infuriatingly tied to a phone number, because the rewrite was really for the Indian market.
My understanding is only Pay in the US and India are the Flutter version, Wallet is not using Flutter. This also had the Flutter boat shaking on reddit a bit back.
They actually wrote the newest Wallet app without Flutter, so it's a step backwards there.