After completing the installation of pre-installed Windows 10 on my computer (CI7 3.6 GHz, 256 GB SSD, 2 TB HDD, 16 GB RAM, NVIDIA GTX 750).
Then I installed OpenSUSE Leap 42.1 from a bootable USB stick (created with ImageUSB/PassMark Software after downloading the .iso file with direct link).
I partitioned my discs into '/' (BtrFS format) and 'swap' on the SSD drive and put the '/home' partition (XFS) on the HDD.
I did not ask the installer to format the EFI boot partition because I was afraid it might jeopardize my system (correct?) but simply mounted the partition as '/boot/efi' (FAT format).
The installation seems to have worked just fine since I did not get any error message.
When I start my system I land in the boot manager offering to boot OpenSuse 42.1, Windows, ...etc.
if I choose to start OpenSUSE, after a short message
0.21...] Ignoring BGRT: invalid status 0 (expected 1)
kwm disabled by BIOS
I arrived to the login menu but cannot log into OpenSUSE (looping login window).
I can login in the console modus (ctrl+alt+F2) but do not know what to do from there...
I cannot login as root because I did not create a root administrator account during the installation (my bad...) and therefore could not try to install a new NVIDIA driver.

And if I choose to boot Windows, I get the message:
filepath: /ACPI(a0341d0,0)/PCI(2,1f)/Sata(0,ffff,0)
/HD(2,190800,82000, ea..., 2,2)/File(\EFI\Microsoft\Boot)/File(bootmgfw.efi)
error: Not supported image.
I identified several threads with similar issues (, but I cannot solve my issue and am not even sure if it is the same problem.

I would appreciate if anybody might be willing to give me some directions here.

Should I re-install OpenSUSE freshly, taking care to create a separate root admin?
Should I ask the installation program to reformat the existing EFI boot partition (FAT)?
Does anybody see some obvious flag in my issue?

Thank you