
There are NSFW communities on piefed.world. One example would be [email protected]. So, it is likely a setting.
If you go to your settings and then the Blocks & Filters page, make sure that you have it set so that you can see NSFW posts. If you have it set to hide NSFW content, then communities marked as NSFW are also hidden as part of that.

It must be I guess. I know that NSFW stuff is hidden by default for visitors that aren’t logged in. I also know that you can set a flag that lets PieFed know that you are hosting sensitive content and it changes some of the default NSFW behavior (for example, this is what fedinsfw.app does).