Google lost the opportunity to actually make it take off, had they replaced the Java stack with Dart, instead of staying in the Java world and adopt Kotlin.
However the Android team was never a great supporter from Dart in first place, hence why you won't find anything Dart on https://developer.android.com.
Google uses Flutter/Dart for their own apps fairly frequently. Obviously not the right choice for the most complex apps. Android system programming and cross platform apps are use cases that are divergent enough that trying to smash them together would result in nobody being happy about the outcome.
Google never pushed Go, the UNIX/Plan 9 and Oberon folks did, as means to avoid doing C++, with support of their line managers as their 20% project.
Kubernetes was originally written in Java, and Docker in Python, it was thanks to early Go advocacy, that those projects got rewritten in Go, and then they got lucky.
Just like the download server rewrite into Go, that was done by someone from Go team, as part of their advocacy.
Check how many public projects does Google do, outside anything related to CNCF project landscape.
Google lost the opportunity to actually make it take off, had they replaced the Java stack with Dart, instead of staying in the Java world and adopt Kotlin.
However the Android team was never a great supporter from Dart in first place, hence why you won't find anything Dart on https://developer.android.com.