The screen flickering is wayland related, so you need to use Xorg as window manager:
- Open /etc/gdm/custom.conf into a text editor
- Uncomment WaylandEnable, if it is commented out, and ensure it is set to false
- Add DefaultSession=gnome=xorg.desktop to the daemon section
- Restart the machine.
source: https://www.serverlab.ca/tutorials/linux/administration-linux/how-to-fix-flickering-in-fedora-on-virtualbox/