If the system recognized this as a disk it would be listed under /dev/disk directory.
If you can provide us with output of the following commands maybe someone can help:
ls -lh /dev/disk/*
udevadm info -q property -n /dev/nv*
If you can provide the output from both arch and obarun live systems it would be even better.
I assume you are booting with a usb stick and have no other drive to boot from?
Do you have a 2nd blank stick to make an installation on and have a persistent real system?
There was an issue in the past, as I read, where some nvme device firmware couldn't provide consistent interface naming, and between boots the device interface name would change causing confusion to the system.
If your device is not found in /dev/disk then partition tools may not work, I think, even if the device is listed in /dev
I wonder what Eric has to say about this. It is probably an issue of eudev hooks needing attention but I can't find much in gentoo or other forums of similar problems and since I have no nvme machine I can't really test anything.
git clone https://git.disroot.org/joborun-pkg/jobextra.git
sudo pacman -S $(cat deps)
sudo pacman -Rnsu $(cat deps)
sudo pacman -U nvme-cli*pkg.tar.xz (xz or zst depending on your /etc/makepkg conf)