I used Dart for a project some 8 years ago. There used to be an easy to use Dart Editor that I used and one day it just stopped working, and stopped getting updates.
Google did not provide any good alternatives, and I just gave up on the language for the lack of developer support. I have not looked back since.
If you liked dart back then, you absolutely should check it out again today. It's improved greatly and easily has the best developer experience of any language I've ever used. Not to mention one of the most rapidly improving.
Non-null by default was a massive change for Dart in terms of perf, and modern dart is quite a different (by very pleasant) beast than dart 1.x.
Google did not provide any good alternatives, and I just gave up on the language for the lack of developer support. I have not looked back since.