No one has (yet) mentioned the main reason I ignored Flutter when it initially came out and why I continue to have reluctance - It's google. They have a terrible track record with products AND with libraries. GWT? Dart (pre flutter)? NaCl? How about all those initial Angular devs? That's not a statement on the quality of the result (though some of those examples do indicate concerns), but if I'm not alone in avoiding…
GWT lived for over a decade (how many web libraries do you know that have survived for for that long?), AngularJS is still in maintenance mode, Dart died when it didn't get browser support and Typescript was obviously the better alternative. At the end of day though, I look at if Google itself is using it extensively, because that's when a library will have the best support/longevity.
It hasn't seen a release in a while because the developers contributing to it have been working on making it work with Google's recently open sourced J2CL compiler. From what I've read, builds of though are available but no official release yet.
I use React and Angular these days, but even back in 2010-2011 GWT felt pretty "done". At least for the things I needed to use it for.
Starting a new project with it now probably wouldn't be a career-enhancing move, but it was a pretty decent way to build really complex web apps at a time when the JS ecosystem was a lot less mature than it is now.