The "sensitive content" checkbox on the metadata tab of your project. That's what determines the NSFW status, not some tag.
Iirc if you select one of the "nsfw" tags, the ones that circumvent the adult setting for browse, the default status of the box is ticked or something to that effect.
And I do not understand what the difference between the two boxes is, that there are. It actually reads, like you can decide if the 18+ warning should be displayed or not. Which would make no sense at all. The lower box is greyed out till you select the upper box.
Audience & Content
- Has sensitive content — This project is not suited for minors or the workplace
- Show content warning — Show sensitive content warning before accessing game