You should be able to post screenshots now. To install OMLx you must have Secure Boot off.
There a number of commands that will show what nvme drives the operating system sees. Like open Konsole (terminal) and type su - to become root and use one or more of these:
fdisk -l
parted --list
May be wise to compare results of these commands between an installed system and the ‘Live’ ISO.
Resources Index Look for the articles under Installation. There you can find:
What to do if there is a problem installing OMLx
That shows how to run the installer in such a way to create a log that could provide information as to why the installer is not seeing the nvme drives on your system. You would post that log here as a .txt file.