Hi everyone!
Someone knows how to fix this or why it’s happening, I usually render in 3000x3000px and it works just fine but this time I need it in 6000x6000px and it’s looking like this.
Data:
Engine - Cycles
Noise threshold - 0.01
Max samples - 128
Denoiser - Optix
Passes - Albedo & normal
GPU - compute
Core i9 10th Gen
RTX 2080 super
Woah. Not sure what’s going on with your render here, but maybe your GPU driver isn’t up-to-date? That’s a random guess, though. 
Kudos for listing your system specs and render settings. That goes a long way towards helping someone diagnose your problem (as opposed to just the render.) Also, you may want to use the Intel OpenImage denoiser for your final render instead of OptiX-- it’s slower than OptiX, but does a better job of preserving detail and minimizing artifacts.
Good luck! 
Welcome to BA 
How much RAM do you have? This looks like a memory error to me
