Thanks for read that topic.
I had posted a topic about NVENC issues.
I have installed NVIDIA-Linux-x86_64-470.86.run in exact same OS and Geforce 600 GPU and now NVENC acceleration is working.
I driver download link not have any information about nvenc fix or changes thus not have information if Nvidia had fixed any nvenc or cuda issue.
Strange detail is in download driver link have a information below
" *This download includes the NVIDIA graphics driver and an option to additionally install the GeForce Experience application. Details for use of the software can be found in the NVIDIA GeForce Software license and GeForce Experience Software license respectively."
Here in forums was posted the information above is wrong.
I not see information about how install Geforce Experience in Linux.
G-Sync was fixed for Geforce 600 GPUs ?
Thanks Nvidia for long time support for Geforce 600 video cards and if was done a fix for nvenc and cuda.
Good seeing Nvidia fixing issues for Geforce 600.
Thus I will continue using Nvidia video cards and recommending for friends mainly because Nvidia support.