To be able to run at 60 frames per second in 4k, even though it's an old game, you'll need a good video card, the one recommended is to run at 1080p, you need one that's stronger than that, in addition to that you said that your cpu ties you up, this is super normal, many games require you to have 6 cores 12 threads at an acceptable speed, then if you're using one with 4 cores 8 threads the fps keeps dropping and going up, it will stay at 60 and 40, 60 and 40, the processor keeps the frame rate always stable at 60, so it is important you would have to change the motherboard and put the processor they ask for in the recommended one, now this gpu that they indicate there is to run at 1080p 60 fps, to run at 4k friend you need a card with at least twice the vram that is written there, the game can be old, it could be a game from 2010, everything that is 4k becomes extremely heavy on VRAM, if to run in 1080p it requires 8GB of VRAM, in 4k it will ask for 16GB, it is always double, then you can try using dlss or FSR, it will run in 1080p and will scale to 4k, it will be a non-native 4k but it will weigh much less, it will be a 4k with 85% of its quality if you put it in quality or ultra quality mode, this resolution is very heavy, it needs a lot of VRAM, using these technologies you can use a video card to have a longer useful life