Gog is the main place for that, since their principal stance is DRM-free downloadable installers. They have a launcher too, but it's optional and only meant as convenience. Itch.io does DRM-free too, but they're often more about very indie and often experimental games. They have a few all-time indie classics though.

Steam technically doesn't require the games to implement DRM, so a part of their library is DRM-free once you've passed the installation process (they don't need steam to be running). This is on a case-by-case basis though. Lots of Steam games use steamworks (Steam's very own DRM) and a lot more use third party DRMs (and even require external launchers like Ubisoft's or EA's).

For years I have been a bit pissed at Steam for opening themselves to all and every shitty fake game/quick buck asset flip there is out there, refusing to do any kind of curation. Instead they opted for letting the almighty Algorithm do that for them. I doesn't work, their store is a discoverability catastrophe full of shit.

That said, I still buy from them in some cases, and these cases are mostly down to one point : the workshop, the integrated mod and user content interface. It's for a handful of games that profit a lot from it, but it's undenyingly convenient.

What I often do if it's a possibility is buying directly from the developer, which often includes a Steam key. That's what I did for Rimworld and Dwarf Fortress (through Itch.io). It gives you everything Steam has to offer for the game and usually a DRM-free version too. Only "down point" is that your Steam review doesn't count for the game's Steam score when you have activated it from an external key. I don't care much for that.

In the end at that point you've noticed I talked about a lot of different platforms and launchers, and it's not even all of them. Like the previous poster, I can't recommend Playnite enough. It's a meta launcher that makes all of your libraries united in the same place, with a lot of options. You still require all the platforms installed, but you're not using them directly most of the time.

I've got Steam, Gog, Humble, Ubisoft, EA, Amazon, Xbox, Itch.io and yeah, even Epic through it (though I only use EGS to get the free games, I don't plan on buying anything from there).