TonyRadX: What follows is an extremely subjective personal rant. Feel free to disagree.
So recently I've had a slight detour from single player games and I ventured into multiplayer and mmo territory for a few months. Specifically I played Warframe, Runescape and EVE Online. Don't get me wrong, maybe I'm just getting old and I didn't realize it until today but I've become bothered with the amount of killing I do in my games.
I realized that most of what I played in recent years revolved around killing - humans and otherwise. And I'm not talking about over the top, tongue in cheek humour games like Postal or games with killing as a main premise like Hitman series. I mean games that old as well as young people enjoy on a daily basis nowadays, like those three I mentioned. Killing in Runescape - check. Killing in EVE Online - check. Killing in Warframe - OMG check. And it's even worse in the last two, since you are basically an immortal killing peeps who have only one life like every other being in the universe (aside from players themselves of course).
I mentioned multiplayer games because, as I said, that's what's my experience lately but it isn't much better in single player ones. I honestly can't name one game I played in recent years, aside from Disco Elysium, that didn't revolve mostly around killing - for exp, for money or just to complete the next chunk of the game. And it doesn't matter whether it's a fairy tale, historical or grimdark ones like Diablo, there's so much killing being done in this industry that it kind of started to bother me. Again, it's very likely that I'm just getting old and this kind of stuff simply stopped appealing to my taste. Nor am I going to become a raving anti-video games activist. I just have to admit, mostly to myself, that it started to kind of scratch at my conscience.
So, today I decided - I'm gonna be more picky about my video games and I'm gonna try to limit the carnage I leave behind me in the virtual realmspace, starting with cleaning up my backlog of point 'n' click games since there seem to be less "k" word in those. So today I start my playthrough of "Beneath a Steel Sky".
End of rant.
Games without characters, like pure puzzle games, might be an option. If there are no enemies (in the usual sense), there's no killing.
VVVVVV is not about killing; while there's something called "enemies", they always move in specific patterns, and there's no way for you to attack them.
Celeste is also light on enemies, and while you do have a way to attack, you don't really kill the enemies, at least not in the usual sense of the word. Even the one boss fight where you have to attack, there's a reasonable interpretation that might not seem as violent.
Undertale is interesting. It does have the whole idea that you can save and reload the game, but other characters can't, but the game is designed so that it's possible to win without killing anyone. In fact, there's even a special endgame path that is only possible to reach if you don't kill anything at all. (There's also a path, one that encompasses the entire game, that you get if you kill everything the game allows you to.)
I remember Waking Mars, from what I played of it, being non-violent, and being all about creating life on Mars (or something to that effect).