But you don't need to know anything to buy a good monitor. And you don't need to run the game at 4K just because you have a 4K monitor.
OP, the advice to buy a 1440p monitor because "that's all you can run" is dumb. Most people keep monitors for at least 5 years and if 4K panels are good quality and affordable today, then you buy that, because in the near future (1-2 years) you will regret not having done so. Buy a 4K monitor as soon as you have the money for it (because you will immediately benefit in all other usage besides gaming), and then when the game comes out weight your performance and GPU options based on your budget. If you can only afford a GPU that runs the game at 1440p, then so be it. At least when the Witcher 4 comes out, you already have a 4K monitor.
Having said that, if gaming is your primary usage you really need to look at gsync/freesync before you bother with resolution.