If installation problems persist see this:
What to do if there is a problem installing OM Lx
Specifically install OMLx from Konsole like this:
$ pkexec calamares -d 2>&1 | tee /home/live/calamares-installation-log.txt
That will create calamares-installation-log.txt which you can post here and may tell us what is missing. Also posting screen-shots helps.
Screen-shots of the partitioning page before and after would help. Are you using ‘Manual partitioning’? That is required to use an existing /boot/efi. Also the /boot/efi must be flagged as boot.
This is unusual. The whole ‘Live’ iso is a squashfs.img. It would be extremely helpful to have that calamares-installation-log.txt to see if we can tell what is wrong. Also you can boot the iso ‘Live’ and check in Dolphin under ‘Removable devices’ and see if this file is present. This is a ROME iso build id # 3081:
