A long time ago, in a distant galaxy...
...there as a thing called Visual Basic 6 (1998). It has a designer, where you drag components (widgets) from a toolbar and drag them on your window (scaffold). External libraries also would appear in there. (video: https://www.reddit.com/r/dotnet/comments/1so2dky/xaml_designer_v06_bringing_a_bit_of_the_vb6_rapid/)
Then, some years later, Microsoft came up with XAML and, after some years after that, the designer was no longer (not even previewer).
Because of that, some people built a Visual designer for XAML here: https://xaml.io/ (you use the buttons Controls, Layout or AI to drag components to the canvas an then use the toolbar to edit the properties (try Position).
More or less doing things as they were in 1998.
I don't know if this xaml.io is capable of that, but back in the day, XAML had the capability of adding dummy data in the UI declaration, so you could preview components with "real" fake data.
My question is:
If this was done in Flutter (as a VSCode extension), would you use it? Would you pay for it?
Notice that this is not FlutterFlow. It is only a designer that generates raw view code (not the entire project).