Comment 12 for bug 1901137

Even the most straight-forward option "Erase disk and install Ubuntu" failed for me on non-UEFI system when installing from USB. I noticed that 20.04 created a single bootable partition while 20.10 creates additional BIOS Boot and EFI System partitions.

The Bug #1893964 Comment #8 workaround (doing grub-install manually) worked for me but after updating I still had to correct /etc/fstab for the /boot/efi device partition.