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.
It would probably be better to have a more general tag system and then NSFW and NSFL could just be examples of tags.
Although NSFW really serves the extra purpose of “18+” which is important to have for legal reasons.
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.