Actually, you do have to.
If this is about the first entry, that game is not marked as adult in the meta data. But after looking at it ... well, you should remember that itch is not in any way kid or family friendly. Decidedly not with all the horror games on page 1. It is 13+ according to tos. And if something is not graphically explicit, it usually is not considered nsfw. The game itself does not promise anything explicit. And adult games usually do so, to increase sales.
If you or anyone else wants to report a game for being nsfw, please consider what standards are to be applied to consider something as "adult". Chances are, it ain't your own standards. The topics themselves are not mandatory adult. It is their depiction. Just look at all the things happening in your typical romcom movie. And what age ratings those have for comparison.