What you're describing is "NSFW" (not safe for work) vs. "NSFL" (not safe for life). NSFL covers the spectrum of anything that could be considered potentially psychologically harmful to someone who's not desensitized to such traumatic things - gore, death, etc. Anything beyond standard nudity / intercourse porn can possibly fall into the NSFL category. For that matter, things that aren't strictly porn can still fall into NSFW, since what's acceptable at some people's work may be stricter than others.
Of course, all of that is dependent on the person submitting the content checking the right boxes. I do agree that the Lemmy devs need to add a NSFL tag to allow instances / communities who want to host such content to be able to delineate between that and NSFW.
https://en.wiktionary.org/wiki/NSFL
https://www.urbandictionary.com/define.php?term=NSFL