In my case, I was trying out Dart because of a Flutter (probably majority of people are now looking at Dart because of Flutter) and I found it really fantastic. I love the tooling where you can just use their CLI to build/test the application without complex IDEs like XCode or Android Studio.
If you want to try building a mobile app then definitely go for Flutter+Dart, even if you don't need to support both Android and iOS I think it's just much more easy to start with than alternatives (RN/Swift/Android Java).