Your first problem will be to acquire a strong graphics card. 3090 for the best.
Unfortunately, such cards are all but unobtainable, even at prices of 2x msrp or more.
On ebay, you can buy them in the $3000 range.
It is the graphics card that is most important for fast action gaming, and particularly at 4k resolution and max settings.
The next thing to look at is your monitor. Many 4k monitors are limited to 60hz, but the number of units going faster is increasing.
What size are you looking for?
LG OLED TV's can run at 120HZ with a stunning image.
Here is a list of 4k gaming monitors:
The processor becomes somewhat secondary.
Newest 11th gen intel and ryzen 5000 series have improved performance per clock which is what most games really need.
You could pick I9-11900K or ryzen 5800x, each with 16 threads which should be sufficient for a high level of multitasking.
If you look at the performance reviews you will see that for 4k gaming, the processor is not the big differentiator.
For heavy multitasking like streaming or multithreaded batch apps, buy plenty of ram.
Intel is not dependent on fast ram for performance.
ryzen is, so plan on the fastest supported ram.