julian_ffm
I vaguely remember setting this up at one point. I had a look for the key (it is still in my boot folder, although I don't use the secure boot at this point).
If you mount the Solus ISO you can find solus-enroll-me.cer inside of efi.img, which you need to mount also. If you boot from the ISO and mount the boot folder it probably can be found in there?
I tried to upload it here, but it's not allowed which makes sense really.