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

[Selur]

I am wondering what is the problem and why my new CPU only utilizes 20 percent  of its capability when converting video.

Okay, using a cpu which offers more threads and probably not a much higher core speed only makes sense when before all the cores where saturated and the processing speed was limited by the account of available cores.

To investigate what is causing the low cpu usage you need to check whether the encoder (or it's settings) or the filtering (one multiple of the used filters) is the problem.

Since you didn't share details on what you do you can do the following:
Create a file with the Vapoursynth script that would be used during encoding and test how fast that would be processed.To do this you would (before creating the job for processing) look at the Vapoursynth Preview (to make sure any used indexing file exists and to check that the script works) and the Vapoursynth Script Preview. Then you would create a test.vpy file with the content of the script shown in the Vapoursynth Script Preview and call:"PATH TO HYBRID/64bit/Vapoursynth/VSPipe.exe" -p "PATH to the test.vpy" NUL in a Windows Command Line prompt.This will do the decoding and filtering of the source without the decoding.While the decoding is running check the cpu utilisation.If the utilisation is low then the used script is the issue. (which is either the fault of one of the filters used, the source filter or the script can't get the source faster)
If the utlilisation is high the speed you see is the max speed you can get and the bottleneck is the encoder.

If the script is the bottleneck share the script with me and may be I can suggest something.
Also note that with newer Intel cpus the configuration on how efficiency cores are used or not might also influence the general speed. (there were a few threads about it over at doom9s a while ago where users reported that depending on their settings they get different speeds)

Cu Selur