It's a "how long is a piece of string" kind of question.
You could game and edit videos in 4K on a bog-standard office PC, depending on the game and how long you're willing to wait for the videos to render.
On the other end of the scale you could easily spend £10k and get something top of the range (dozens of cores, several beefy GPUs, etc.).
Depends on your gaming demands and patience. (Always is tbh, nothing special about 4K.)