Maybe a setting for each tag for whether it qualifies as NSFW? That way you could have multiple tags that would be filtered as NSFW for different classes of content, which could enable individual users to only filter one of the tags if they only want to avoid something specific.
I've made a post a few days ago. I'd argue we should make a proper distinction. Adult content and NSFW isn't the same thing. Currently everything from sex education to gore and death is the same category. I think it's really not. NSFW tags help so you can scroll through things in an open-plan office or while commuting. Porn is porn and gore is gore. I think we shouldn't oversimplify this but keep the nuances and have different categories. Also I'd like to not mix stuff like sex education which might be fine, and minors ask those questions all the time on Reddit with other things like fetish.