Just about any GPU will be good enough to play TS4, it's not very demanding when it comes to that. It still works on integrated graphics, but yeah, there's a noticeable drop in performance. I use an RTX 2060, and even though it's an older card, it's still overkill for TS4.
Keep in mind that TS4 is very CPU-intensive---if you're buying a pre-built PC, make sure the case is very well-ventilated, or it will run quite hot. Many manufacturers sell prebuilts with a flat front that has no ventilation--don't buy one of those.
And I would consider 8 GB the bare minimum....if it were me, I wouldn't run any less than 16