Veteran Chinese users, with some sense of bewilderment, welcomed their American counterparts and swapped notes with them on topics like food and youth unemployment.

Occasionally, however, the Americans veered into riskier territory.

“Is it ok to ask about how laws are different in China versus Hong Kong?” one American user asked.

“We prefer not to talk about that here,” a Chinese user responded.

Such impromptu cultural exchanges were taking place all across RedNote, known in China as Xiaohongshu, as the app surged to the top of U.S. download rankings this week. Its popularity was driven by American social media users casting about for an alternative to ByteDance-owned TikTok days ahead of its looming ban.