The longer I think about this, the less I understand the two checkboxes.
And what is the difference between having only the upper or both being checked. If only the lower were the true nsfw checkbox and would have to be marked manually, why not preselect it too? And what sense is there to claim content is sensitive but not display the sensitive content warning? The second checkbox does not assert anything about the content's sensitive-ness. It almost reads like Itch would give control to the 18+ warning to the developer - after it was established that it is 18+ content.
There are several places on Itch webpage where, what is written is misleading, if taken literally. Like the simple "Search for games or creators". You can search for non-games there too, and creators no longer - but for games by creators, which is not the same. And you will search for titles and not games by search topics as used by internet search. Or the tag box that says, Select a tag. It implies that the list is all the tags and does not look like you can write in it for more than quick-selecting the long list.