World Anvil Grandmaster here!
I really enjoy it as a wiki, but keep in mind the primary audience and user-base is for TTRPGs, so novel wikis generally get less attention than TTRPG-focused ones. They also support manuscript uploads for authors, and while I have some current issues with the implementation, there is a major update for that functionality coming, so I'm going to keep my peace until after the update.
I primarily use it as a story bible for myself, and it's pretty good in that regard. The biggest asset it has, imo, is that it has a very supportive and active community. You'll get more out of it by joining the discord and finding people on-site you gel with than just posting and doing nothing. The frequent events are also helpful in getting you out of your head in regards to world building, and all are free to enter with some including prizes! (Most offer onsite badges, but the big competitions offer material prizes offered by community judges, including: merch from TTRPG and related stores, story writing courses, art by an artists for your work, world building tools, etc.)
It's also a pretty small dev team, which is why I mildly grump but fully understand that they focus mainly on the TTRPG features first, since it's the vast majority of their user base. They do allow nsfw content, I think it's just the legal definition of porn that they don't allow (ie, images depicting real people sensually naked/engaging in acts). I would have to double-check to be sure, but there is a toggle for marking content nsfw and I know non-sexual nudity is allowed. The dev team is also available in the discord and very responsive, the two founders often pop in the check things.
They do offer a free option, by the way - it's not all paid. You'll get all the basic wiki functions with the free version, you just run out of space eventually and don't get all the bells and whistles. So checking what you need is a good idea re: functionality. I paid because I have a lot of content, and I upped my subscription to lifetime because I do see myself continuing to use the service for a long enough time to make the cost worth it for me, but that's all up to you. But you can always start free and see how it goes from there.