Discord is blocking users of its iOS app from accessing servers that are tagged as not safe for work (NSFW). Communities that focus on adult themes or host mostly mature content are behind an age gate so users aged under 18 can't access them. But now all users have been locked out of those servers completely on the iPhone and iPad app.
You can still access NSFW servers on iOS through your device's web browser, though the features are more limited. As Apple Insider notes, an updated community notice that announced the change didn't mention the reason for the move, including whether Apple asked Discord to block NSFW communities. However, it appears that users of the Android app can still access those servers.
Discord has reportedly been in talks with potential buyers, with Microsoft said to be discussing a deal worth over $10 billion. Cutting out adult content might make the chat service more palatable for potential suitors, but that doesn't appear to be quite what Discord is doing here, given that NSFW servers are still accessible on other platforms.