Buildapc

It's mostly kernel upgrades that can be a problem. If you stick to the repo, you will generally be fine. If you need a specific version of CUDA, or a feature that's only in the newest driver release, you'll have to build the kernel module yourself. It's not a huge deal after you learn how it works but you're almost guaranteed to break it at some point and then you're on the command line. If that scares you, go AMD.

Fyi an alternative to Playnite with a similar goal is Lutris. You can even integrate several platforms like Steam and GOG to download games directly through the Lutris interface.

On top of that, it's super easy to install games via exe's, custom install scripts, add existing install folders, etc. The UI is a little bit spartan compared to Playnite, but it's very powerful.

I say this because, among other things, a huge benefit of Linux is that it's great for older hardware. From the sounds of it, you aren't looking for the latest and greatest in terms of build specs, so Linux may be right up your alley (also no built in spyware, ads, forced online connections, and resource hogging processes that can't be disabled).

Right, huge price difference. Performance isn't totally linear like this, but it's still helpful to think of it in terms of pixels and fps. 4k is for times the pixels of 1080p, 120fps is twice the frames. So to go from smooth 1080p 60fps to smooth 4k 120fps you need 16 times more graphics power.

Your screen resolution and fps goals (capped by your screen's refresh rate) are something you want to nail down. I think the jump to OLED 120hz or higher screen is better than 4k partly because getting high fps out of 4k is much harder.

A $1500 budget can go a long way. Don't think about future proof, think about meeting your goals in games today, whatever you build will be fine for 8 years as long as your standards don't change. Outside of pushing 4k and high fps, graphics demands have plateaued compared to 10+ years ago. Ray tracing was the last big wow, and AI processing in the pipeline has done wonders at improving performance. I don't see the value of a motherboard that costs more than $200, and the best value CPU for gaming is the 7800x3d which is $400 when not on sale. You don't need more than 32gb of RAM, decent kit is about $100. Cases are looks subjective, airflow objective, runs $30 to $150, up to crazy high for gamerz styles. Any PSU over $100 is a waste of money, even driving a 4080 super. For storage get a well rated NVME within your capacity goals, $100 gets you a good brand with decent space. That would leave $500 for a graphics card, buying new won't get you top of the line, but you could get last generation's best with that. If you live near a Microcenter and can wait for a good bundle, you can save a few hundred. Sorry for ballparking, writing from my phone. Use pcpartpicker and have fun with it.

Higher frame rates and higher resolutions and better settings. The better your machine, the higher settings you can use, which looks nicer. For $1000-1500 you should be able to go up to 1440p. It depends on what kinds of games you play. If you play competitive shooters, a higher frame rate will be a real advantage. For pretty much everything else it's all about the eye candy.

Edit: here's a video with a few build examples. This channel is pretty good for choosing components to get the best performance for your money.

https://youtu.be/oICZZrVmlzk?si=DpbRmWdNWJIqEE5k