Zorin OS 16 Core random freezing on Nvidia

A few things you can try:

sudo prime-select nvidia

On Demand may cause crashes.

You might try the grub parameter intel_iommu=off if you are using Intel integrated with Nvidia dedicated.

You might refresh the Nvidia drivers (I agree about 535 drivers being itchy):
Thoroughly remove Nvidia drivers

sudo apt remove --purge '^nvidia-.*'

Install Nvidia drivers

sudo ubuntu-drivers install

Add X-Swat team repo

sudo add-apt-repository ppa:ubuntu-x-swat/updates

Upgrade Nvidia Drivers with X-Swat updates.

sudo apt update && sudo apt full-upgrade