In this situation however you're suggesting to make a separate page for the free demo because the full game can't be indexed. This goes against guidelines in two different ways. It might not be a good idea.
Viewing post in NSFW Demo Question
...The quality guidelines that you should be familiar with already.
In fact after doing even more research, you, yourself say I can do it either way. So I will choose a project page for the demos.
https://itch.io/t/1564349/how-to-handle-game-demos
So, looks ok.
I asked in a few discords as well with other content creators, and they have also done this, as Itch itself, in its public statements about NSFW seemed to literally be asking us to do/implying for us to make things for free to get relisted. When I first asked this today, I had only started looking into it.
I should add, why I asked was because I didn't know if I keep them on the page with my paid games, if that means since it will have a free demo (not even sure if I can set the demo to free on the same page as content set to paid), but I was asking would it get listed if it is on a page also with paid content.
So, in case, based on how you are kind of coming off, let me make sure you understand, I am not ignoring your advice or typing any of this with any kind of vitriol or meaning to come off any anything less than grateful to you, but after 12 hours looking into this I am learning a lot. It sent me all over the place, but the more I have learned the more it looks like setting a separate page as a demo appears to be the cleanest and most likely to get people to my paid games (which makes money for Itch too, I've paid thousands of dollars over the years, I could have kept, and chose not to do so as an honorable person).