App icons are the most visible part of your store listing and Apple holds them to strict standards. Nudity, violence, trademarked logos, and certain other content types will get your icon rejected before reviewers even open the app.
What Apple said
“Your app icon contains content that is not appropriate for the App Store. The icon includes imagery that is offensive, contains a third-party trademark, or does not meet our content standards. Please update your app icon and resubmit.”
Your app icon is visible on everyone's home screen — Apple treats it with a higher content standard than app content behind an age rating. Even a 17+ app can't have an explicit icon. Trademarked logos from other brands, suggestive imagery, or violent imagery are all disqualifying. The icon also needs to be original art, not something you grabbed from Google Images.
While you're at it — Apple also requires these pages for every app.
Fix this rejection, then make sure you're covered on the compliance side too. Apple requires every app to link to a hosted Privacy Policy, Terms of Service, Support page, and Data Deletion page. No link means another rejection — just for a different reason.