I vaguely fondly remember a time when Google Play (Google Store back then?) was pesturing me to leave a review every time I was uninstalling an app.
How can I enable this feature in Android 6?
This is a Google Play Store feature and is not dependent on the Android Version
Features of Play store which frequently change or sunset and there is no way to revert to earlier behaviour. For instance, Play Store asks for a review as mentioned here, a feature earlier not present Why has Google started asking questions when reviewing apps in Play Store?