This is a known problem with some computers. I used to have that problem with a Lenovo, but a BIOS update fixed.
Booting linux with secure-boot depends on shim (the file “shim.efi”). The openSUSE “shim” has two signatures. It is signed by Microsoft and it is signed by openSUSE. Unfortunately, there are a few computers with firmware that does not properly handle a shim with two signatures, and some ASUS computers have this problem.
There is a workaround – just remove the openSUSE signature from “shim.efi”.
Check this web page: openSUSE:UEFI
and scroll down to look for the section “Booting the Machine that supports only one signature with vendor provided Keys”.
Personally, I found it easier to just disable secure-boot. Now, with an updated BIOS, I leave secure-boot enabled.