iOS and android support for detecting if app has been rated from within Unity

I would like a bonus level to be available for users who have completed a rating of the app on the store. Is there a way to do this from within Unity?

Not possible.

A proper alternative can be asking for user to review with “Rate Now”, “Later”, “Never” options. If he clicks on Rate Now, most likely you can consider he will rate with more chances.

Make sure you won’t prompt that alert too often too.