Bought new 12700K CPU bit Hybrid only utilizes 20 percent of it

[Selur]

@4K@60FPS:

also when converting 4K the whole PC becomes very laggy.

Hmm,... system should not get laggy, since Hybrid usualy calls everything with 'idle' priority.
you might want to check:
a. to input, temp, output folders lie on different drives?
b. is there something else using the disk?

About cpu usage with 1080p:
How is the cpu usage distributed between (vspipe,encoder) when you encode 1080p and 4k?

Assuming SVP is the bottleneck, you you try tweaking the SVP parameters, read: https://www.svp-team.com/wiki/Manual:SVPflow

Cu Selur