If a desktop is showing a black screen on boot, several things could have gone wrong.

If the desktop is using the nvidia drivers, check the troubleshooting tips on the Nvidia driver installation guide:

https://forums.freeside.co.uk/t/installing-nvidia-drivers-on-fedora-30/193

If not, then check:

  1. ….to make sure that the nouveau driver is actually installed.
  2. That the nvidia drivers are not installed: dnf list installed | grep -i nvidia