It is an interesting concept, edge, in RPGs. Of course, the edge should be just a little bit over there, just out of sight.
I can see no point at all in making any player in any game I run feel uncomfortable, or even worry that the direction the game is going in may get uncomfortable.
You should never even get close to the edge.
In solo play, edginess is kind of academic. You are in control and you include or do not include whatever you want.
What I have found interesting is that I have certainly played games in solo that I would never even contemplate offering to my group.
My face to face group, when we used to be able to meet, were very traditional. Dragons will be smited and princesses will be rescued.
As a counterpoint to all the dark stuff in the Cthulhu games I wrote for this month, I was playing Visigoths vs Mall Goths. I wrote a very brief set of solo rules for a Goth vs Goth game jam over on Itch.io. They are free or at least PWYW.
Visigoths vs Mall Goths is a cute little game. Interestingly, so far this year, I have only played two games where being non-hetrosexual is explicitly mentioned in the rules, and both games dealt with that coming of age period, and both focused on emotion harm over physical harm.
I mention this in the #RPGaDAY2020 Edge article because, in both games, player safety and their wellbeing is the absolute paramount concern. They are the absolute opposite of edgy. They are excellent examples of safe places. Tales from the loop can be quite hard hitting but long before that ever comes up, the safety tools, lines, veils and the X card are right there at the top of the game.
In fact, I think that these two games, Tales and Visigoths are the first time I have seen safety tools in a game that I didn’t write.