Replace nouveau with the Nvidia driver
If a fresh install boots into the nouveau driver, swap it for the proprietary Nvidia one.
ubuntu-drivers devices
# Install the recommended driver:
sudo ubuntu-drivers autoinstall
# OR, pin a specific version from the previous output, e.g.:
# sudo apt install nvidia-driver-535
sudo reboot
After reboot, verify:
nvidia-smi
lsmod | grep nouveau # should print nothing