The Ubuntu Release Notes, https://wiki.ubuntu.com/FocalFossa/ReleaseNotes#Installer_and_live_session, mention an issue with nouveau crashing during the installation process. You might take a look at those and see if the work around helps you out.
** Package changed: ubuntu-release-upgrader (Ubuntu) => linux (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1875266 Title: Installation of 20.04 fails with a kernel bug To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1875266/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs