You need to enable IOMMU-virtualization in your BIOS.
It shouldn’t prevent Qubes OS to boot if not enabled, but you will miss some Qubes security features.
https://www.qubes-os.org/doc/installation-troubleshooting/#unsupported-hardware-detected-error
It will be saved into the EFI partition.
The command should be as follow:
efibootmgr -v -c -u -L QubesOS -l /EFI/qubes/grubx64.efi -d /dev/sda -p 2
it’s not -d /dev/sda2, just -d /dev/sda.
I you want a space in the name use quote (e.g. -L 'Qubes OS').
and as mentioned by disp6252:
in this example, your EFI partition is -p 2 and the disk is -d /dev/sda.
You could try:
https://www.qubes-os.org/doc/uefi-troubleshooting/#installation-completes-successfully-but-then-boot-loops-or-hangs-on-black-screen
You could also try:
https://forum.qubes-os.org/search?q=black%20screen
There is a lot of forum post, you have to search and try, as only you have access to your hardware. 
You could remove quiet from the kernel option to have a better logging of what happen.
You could try to install with the latest-kernel option from the installation USB.
You could give a try to Qubes 4.2-rc3. It’s stable enought to be used as a daily-driver.