Just started some more testing on looking at 1864787, and an OEM setup option appeared in the GRUB screen on the uEFI box. It appeared to only Start the live session only, ie. https://bugs.launchpad.net/ubuntu/+source/calamares/+bug/1901056
Neither focal, nor focal-1 release notes mention OEM not working.. maybe that should be mentioned.
The OEM setup is NOT seen when booted on BIOS boxes.