RedNote, or Xiaohongshu, is a popular Chinese social media app. American users are flocking to it as TikTok faces a looming ban, pushing the app to the number one spot on the country's app stores.

Tens of millions of American users of TikTok who are girding for a ban of the app are migrating en masse to another Chinese-owned platform that has emerged as an alternative. RedNote, which is ...