‘Good on You!’ Means ‘Well Done’

In everyday Australian English, Good on you! usually approves someone’s achievement, decision or action. It is close to “well done” or “that’s great”, not “this is beneficial for you”.

A: I finally finished that evening course.
B: Good on you! You stuck with it.

The phrase can congratulate a result or support something worthwhile that a person chose to do. Good for you is more common in some other varieties of English and can carry a similar meaning. If you literally mean that something is beneficial, say It’s good for you. Good on you is usually warm and sincere, but a drawn-out delivery or sarcastic context can reverse its attitude, so tone still matters.

https://dictionary.cambridge.org/dictionary/english/good-for