Ubuntu 18.04 server AMD64 (and 20.04) can't raid 1 root partition

[Leroy Tennison]

When attempting to install Ubuntu 18.04 server (or Ubuntu 20.04 server) only UEFI configuration is available even if the drives are smaller (240 GB) than what UEFI is required for.

In the installer (either the default or updated one):

If I select "Use as Boot Device" for a device then the device is not shown as a device for "Create Software RAID"
If I select "Use as Boot Device" for a device and "Add GPT Partition" (to create an unmounted partition for root) then I can't select a specific partition in "Create Software RAID"
If I create a software RAID (mirroring) first then it can't be selected as a boot device

I have searched the web and what I have found (including the Ubuntu RAID guide) is either outdated or wrong.

I'm now looking at installing Ubuntu without RAID then attempting to create a RAID of root after reboot but I can't seem to find how to do that either.

Preferably, can you provide instructions (or a URL to same) for either method? Otherwise this needs to be considered a bug and resolved.

The only work-around I have found is to install Ubuntu 16.04 and use BIOS/Grub to create the raid then use do-release-upgrade to move to Ubuntu 18.04. Unfortunately, this isn't working on some hardware.

I can provide screen shots if needed.

Thank you for your help.