Hi, i have some news about this !!!!!
After completing and sending the “NVIDIA display driver form” corresponding to the 2 lastest driver releases, 2 weeks ago i reciebed an email of [email protected] asking me to send them the full kernel memory dump to try to investigate it, and i did it.
today i recieved a new email saying:
I have added the bug to the open issues list on our forums for tracking purposes:
Displayport-to-HDMI 2.1 protocol converter clock limited to 600MHz pixel clock 
So hopefully, nvidia driver team is now aware of this issue and will try to get a fix for it 😉