In my experience Darti s not a problem at all. It's a simple boring javaesque language you can learn relatively quickly if are already proficient in other languages, plus you don't really need to use all features of Dart to create multiplatform apps.

What if more difficult is Flutter itself: you basically need to learn everything from scratch: the architecture, they way to write apps, plus all the library functions you may need. My experience is that this particular aspect took me much longer than learning Dart itself.

Or GDScript, Godot’s language, which nobody knows. This is my major barrier to even considering Godot right now. Perhaps once their Kotlin bindings are ready for production…