Right click on a game link to open in a new incognito window. If the message about 18+ appears, it is marked as adult. If not, not.
And some of those things are not nsfw at first glance. Itch requires "strong adult themes" to be marked as adult. But is lacking a definition for strong, for adult and for strong adult.
The wording with strong adult implies that there are adult themes that do not need to be marked as adult. Non graphic sex maybe. Or naked feet. Cleavage. From the other side, a pure text based game can have strong adult themes too, depending how graphic the themes are.