Short answer, no. Marking an episode as mature doesn't do anything other than warn people before they see the actual episode. It shouldn't prevent you from appearing in Fresh, Trending, Popular, etc, according to how those things normally work.
In some cases mature stories are pulled from the app but still appear on the website. This doesn't seem to be based on if you happen to mark some episodes as mature, though. I think it's based around key search words in your tags, and manual review. But obviously there's pretty limited information about this. It also probably affects comics way more than novels, so if you're writing, I wouldn't worry over this too much.