I got it working. Thanks.   Edit: Use Clover.
I've been pulling my hair out trying to get Proxmox VE 7.2 to boot from my M.2 drive. I was able to select and install it to the drive via the Proxmox installer (after having to throw in a GPU because it changes video output to something that won't go over the VGA port midway trough setup). However the BIOS shows Proxmox in the boot options as unavailable, and when it tries to boot it does try the Proxmox install but it says boot failed. "Booting from proxmox" "Boot Failed: Proxmox" "No boot device available or Operating System detected." "Please ensure a compatible bootable media is available"     I have updated the BIOS. (2.15.1) It is in UEFI mode. The NVME BIOS setting is set to non-RAID. I have tried "Auto Discovery of Bifurcation", "Platform Default Bifurcation", and "manual 4X" options. I've tried Slot disablement option "boot driver disabled" and "enabled" The Drive is a Intel 660p Series M.2 2280 1TB PCIe NVMe 3.0 x4 on a Dell BOSS PCIe (2X) M.2 card (PN: 23PX6 NTRCY).   I have found something about using Clover, but I am unsure if it will work for my newer 14G system, or if it is of any use to my situation. (I had a link to the article but it wouldn't let me post it)
Dell T440 Proxmox Fail to Boot (PCIe NVME)