Your question is Significance of Engagement Impact. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Explain how you would assess the statistical significance of a new feature's impact on user engagement.
Describe how you would define the engagement metric, randomize users into treatment and control groups, select an appropriate statistical test, calculate a p-value and confidence interval, and make a decision at a prespecified significance level. Address assumptions, practical significance, power, and risks such as repeated users, novelty effects, and multiple testing.