Nudity, gore, violence - explicit materials. Stuff you wouldn’t be allowed to plaster on a giant billboards in the middle of the city or on the side of your office building or have run on daytime TV in the breakroom. If an image of a clothed female is NSFW then obviously a man wearing nothing but a towel in a shower is as well.
You start making a list of everything everyone takes offence into and finds inappropriate and you end up with a list with literally everything on it. Some people in this thread have used “If I couldn’t use it as a wallpaper at work, it should be NSFW”. Plenty of people would find this picture absolutely disgusting and inappropriate, so should it and everything like it be NSFW tagged as well?
It is still in early access and optimising the game is their current goal according to the road map, though as the whole concept of the game is about simulating every NPC properly at all times it’s always going to be really heavy game to run.
And you are right about accessibility making resource hungry games more common - they allow indies to make projects and use concepts that would have been scrapped as technically non-viable by a publisher before. Shadows of Doubt started development back in 2015, which would have meant reducing the scope of the game until it ran on a PS4. Being indie, they could just do whatever instead, and now it’s going to be enough if they can make it run acceptably on a PS5.