Where to get games without installing a store client?

I've been a console user since forever but I've somewhat recently gotten a strong PC that I'd like to install a couple of games on. I installed steam about a year ago and didn't like that it was always running in the background so I uninstalled it a couple of months ago. I play super infrequently, I don't need something that starts automatically and runs all the time. I don't WANT something that starts automatically and runs all the time. I just want to be able to play things like Kerbal Space Program from time to time and not have anything eating system resources when I'm not actively using it, MS365 does enough of that on its own.

Is there somewhere that I can just buy a game and have it installed locally and play when I want without needing to use a store client or are those days long gone?

Edit: If you're going to tell me to just unselect "start on startup" it didn't actually work. Steam store didn't open on startup, but the client still did. Ending the task in task manager would shut it down for a few seconds and then it would come back. It very much felt like an "okay your computer is a steam machine now" application and that is not at all what I want, it's a workstation first.