Is EFI Partition really needed?

I am installing 20.04 to a new SSD. I already have 18.04 installed on its own drive which does not have an EFI partition. During the installation process, I selected "Something else", New Partition Table, Primary, EXT-4 and selected "/" as the mount point. When I continued I got the following notice:

No EFI System Partition was found. This system will likely not be able to boot successfully, and the installation process may fail.
Please go back and add an EFI System Partition, or continue at your own risk.

Do I really need an EFI parition with 20.04. Below are screen shots of my disks.

If you started the install in UEFI mode, you will need an EFI partition. But, if you started the install in Legacy mode, you don't need it.

How can I start the install in legacy mode?

I downloaded the ISO and made a DVD for installation. Same exact process as I did with 16 & 18. Could the DVD be starting in UEFI mode?

While booted to 18,

$ if test -d /sys/firmware/efi;then echo efi;else echo bios;fi
$ if test -d /sys/firmware/efi;then echo efi;else echo bios;fi
$ ls /sys/firmware/efi
ls: cannot access '/sys/firmware/efi': No such file or directory

My understanding is that the DVD has both legacy and UEFI installers; if the BIOS setting is to boot UEFI (windows stuff), then DVD will start as UEFI. If you go into bios, it should show two boot devices for the DVD, one UEFI and one legacy.

To verify, start UM20.04 live and run the test you showed above. It will tell you efi or bios.

Thanks. Booting to the bios I have the option to boot the DVD to either UEFI or Legacy.