The trick above works even better than expected: it also works on a stock Ubuntu 20.04!
- Install Ubuntu 20.04
- Do all the updates
sudo apt-get install nvidia-driver-495
- plug the eGPU
- run
nvidia-smi
to verify the GPU is detected - install and configure egpu-switcher
- power off
Then the trick:
- unplug the eGPU
- boot to GRUB
- plug the eGPU
- boot Ubuntu
Done!