By renaming the NVRLA.EXE to NVRLA.EXE_OLD gave me back my good framerate as that process was blocking most of my CPU power and was producing a lot of stuttering and at the worst 5 fps and blocking the app completely.
Uninstalling GeForce Experience at this point didn’t contribute more positively on the system as the NVRLA was already disactivated.
As a result now everything is smooth as butter.
SU6, few clouds, resolution 4K 120hz, all settings ULTRA and LODs 200 + 400: smooth 44 - 50fps