@meiko60 why do you think that the reason for the freezes is the graphics driver. Isn't Linux completely freezing typically a running out of RAM (when you haven't set sufficient swap partitions or swap files). On KDE, you can enable the classical Ctrl+alt+del key to reset the xserver/Wayland (advanced keyboard options). Could you check whether this still works when the freeze occurs? Are there any special things in your system log?
@meiko60 newest Nvidia drivers are at the moment 535.xx. you could maybe try upgrading to se whether the situation changes. It's easiest to get new Nvidia driver when following the instructions for installing CUDA. You typically don't need to install all of the CUDA SDK and could for instance just install the package cuda-drivers