Hello.
I’ve found this thread while searching for my issues.
I wanted Ubuntu Unity installed in BIOS mode but kept getting the terminal with OP’s output.
not even the shutdown command was being recognized.
Following @Maik 's link I’ve downloaded the 20.04.03 from /bios/ folder.
Alas, the results were the same.
Fufus 3.17 was my usb burner of choice thus far and I decided to play with a few settings.
What worked for me was I left all the settings default (MBR/volumename/etc) but in prompt where it asked about MultiISO format, I selected the 2nd option (DD - not the recommended one) which upon completing the writing process did not provide me with a USB drive with FAT32 system (in contrast to rufus’ recommended choice), but something invisible to Windows.
This seems to have made the trick as the USB successfully launched Ubuntu in Legacy Mode and currently installing the system on the main drive.