Comment 10 for bug 1901137

My bug report #1902269 has been marked as duplicated of this one even if the description it's not exactly the same.

In any case it looks the problem is related to the EFI (ESP) partition, that should never be used on old BIOS or UEFI in Legacy Mode, but for some reasons the installer want it... even if we are NOT in "UEFI mode".

This might be related to recent changes of the installer https://discourse.ubuntu.com/t/groovy-to-use-grub2-for-booting-installer-media-in-any-modes-on-all-architectures/16871
You have probably noticed that now there's no difference between uefi or bios mode. When you boot the live USB, you see the same grub menu.

After many tests, these are the case where the installation has been successful:

- updating the system directly from Focal (from 20.04 to 20.10)

- creating an EFI partition during manual partitioning.
In this case the partition must be a primary partition.
(One user was able to set the EFI partition on a USB drive... it was not my case).

- Installing Ubuntu using the "Erase the disk and install Ubuntu.." will also succeed. EFI partition will be automatically created.
(Also the option "Install Ubuntu next Windows" should work, but there must be enough space for a primary partition for the EFI).

As reported on bug #1893964 (comment #8), the user was able to install the system skipping the "grub-install" launching Ubiquity with the command:
ubiquity -b
Then he manually recovered GRUB. I've tried the same, but with no success... still had problems with efi. The log reported several errors and one of them was:
## pc systemd[1]: Dependency failed for /boot/efi.
## Subject: L'unità boot-efi.mount è fallita
## Defined-By: systemd
## Support: http://www.ubuntu.com/support

I hope there will be a solution as soon as possible, this is one of the worst bug ever :(
The only lucky thing is that Ubuntu 20.10 is NOT a LTS... other wise many more users could have been in trouble.