Go to your settings and ensure show NSFW communities is enabled. Once active, you should be able to see nsfw communities in the list, denoted by their blurred icons by default.

I made a small list of NSFW furry communities here

The developers of lemmy are very anti-NSFW, it shows up in some ways everywhere. One of those ways is you can’t see NSFW on community lists outside of your own instance. You can use outside sites like https://lemmyverse.net/communities to get around this. I think everything might be listed directly in the API request too, but its been a while since I played around to check it out.

Seems like using an app for lemmy (mlem for ios) is what caused this, my bad for not checking that first.