There is a Flutter documentation page:
https://docs.flutter.dev/release/breaking-changes/android-java-gradle-migration-guide
But you can completely ignore it and follow this article which is the best i have found.
Flutter is no longer compatible with older versions of java, so you need to install a new one and make sure you configure it so your IDE can access to it (path, IDE, Android Studio...) There's plenty of help online now and via AI Agents