Same as most people. OSs have just evolved to become systems made to serve their creators rather than their "customers".
Windows wants to steal all your data and then use it to shove ads in your face.
Apple also constantly tries to push their own products and services through the OS, not to mention continually pushing the boundaries of irrepairability and locking you in an ecosystem. And just being extremely expensive.
I don't understand. You say you need it, and then you say you've never used it. How would you know? I can confirm it's absolutely not needed. And it will only make shit harder.
There are a bunch of great build suggestions on the homepage of PCPartPicker. Really the only consideration if you want to use Linux is to go with AMD for your GPU (they're usually a better value anyway).
I wouldn't recommend any prebuilts, they're usually not a good value. Plus you can learn a lot about computers if you DIY and it can be helpful to diagnose in the future.
If you choose a case without a transparent side panel and ignore RGB and glamorous components, you can get better performance.
If I have to be complicit in order to encourage others not to be complicit, then what's the point?