Fresh download of Focal, verified SHA256. Boot from USB on my XPS5 test PC, all looks fine until the point where one can "Try" or "Install". Screen is tearing so badly, it is difficult to hit "Try". If successful, load continues to a desktop that is malformed, tearing and is an odd yellow and violet color. Top bar is visible, but attempting shutdown via the icon does not work. Ctrl-Alt-T accesses terminal to shutdown from there.
Ubuntu 18.04.3 works fine on this PC.
Dell XPS5, 4GB RAM. Nvidia GeForce 6800
No one else is reporting this issue from reading screen tearing posts. Solution?