So I'm planning to make a NSFW game and I figured it should be separated from my main account. At the same time, I'm also planning a SFW version and that version will be released here.

Is doing that allowed here on Itch.io?

The devs that do that usually do that on one account.

It depends on many factors, if using two accounts would be wise. Or if it might even be unwise to not do so.

In my opinion the main issue is, if your sfw version will be marketed towards children or not. Or if it is just sfw for technical reasons, but the audience is still adults. Also, Itch might disagree, since nsfw is only vaguely defined. And if you split your accounts, you split the followers and ratings.

A "streamer" mode might do the trick. Big games that feature nudity often have such. A configure option to make the game safe for streaming.

If you make several games, it would be wise to split your audiences into "family friendly games" and nsfw games. But you say you want to make a nsfw game that has a sfw version.

And if you use your account for other things than publishing, please note, that you cannot configure your account to not see nsfw games, after you have released a nsfw game.