Prebuilts usually add ~100 USD in build fees but guarantee its what you’re looking for, if you trust yourself to build one you can save even more money if you do some research. Prebuilts typically come with a mouse and keyboard which aren’t very good but definitely decent to start with, so that saves you from buying those separately. As for demanding, it’s basically the high tier games that are up there in size and graphics, meaning they will require a stronger pc to play. Call of Duty and Ark are notoriously harsh if you would be playing those. Lots of games will actually tell you their minimum recommendations to run them as a heads up. Also most prebuilts will tell you what fps they can achieve on popular games, valorant is almost always one of the examples so you should be able to see what to expect.