what videos are those? flightgear looks like ass without mods so maybe it’s modded? also flightgear runs on a baked potato so i wouldn’t worry too much.
when it comes to building a machine, you’re unfortunately going to have to deal with rgb. the supply/demand situation has gotten us to the weird place where components with christmas lights on them cost less than those without.
not really, unless you get like a mini pc. you usually don’t save much money at all on prebuilts. maybe look into refurbished or second-hand machines if your setup is very old?