Yet another answer ...
one more way to
avoid UEFI in a fresh & recent installation w/o upgrading:
Goal: Have a fresh install of the latest Version (currently U21 and counting) on your hard disk without UEFI.
First install some old Ubuntu 12 or 14.04 version in some free space. This is definitely free of UEFI.
Make sure you can boot this stone-age version! If necessary create a boot record on USB memory stick (!) to be absolutely sure. This can be done easy:
sudo update-grub && sudo grub-install -v /dev/sdk (adapt USB-media name!!)
Test it. Make sure you can boot the stone-age version!
Then install the recent version like U21 Hirsute Hippo without(!) a boot option.
This option can be chosen in the installer GUI where the device for the boot record is chosen.
Boot U12 (or 14) and run update-grub, install grub. Just like
sudo update-grub && sudo grub-install -v /dev/nvme0n1 (adapt disk name!!)
Now you can boot the new Ubuntu version without UEFI :-)
In the recent version do install grub, then run update-grub, install grub like before.
Later you may delete the temp U12 partition. Use gparted (safe and capable).
If its in on extended partition you need to boot from external memory stick or DVD because of the mount and swapoff issues.
You are right if you think this is a kind of change root for dummies process.
Very pimitive, not much risk, proven to work.
If you like it please consider to upvote the entry :-) Thanks!