Curious abut the new version 15.5, I upgraded my laptop from 15.4 from a bootable usb-drive with the 15.5 xf-86 DVD iso image.
Installation process (upgrade) seemed flawless. However, after rebooting the system, no Plasma (X11), Gnome or ICEwm did start.
Instead, a terminal was opened top left of the screen. No window manager.
When, from the mentioned terminal application I logged in as root, and the did ‘startx’, the Plasma desktop does start-up.
For a normal user, startx just gives a black screen, but with the mouse pointer active!
Instead of an upgrade, I tried a new, fresh install.
The same useless result.
As a bonus, after several boot attempts, I now get a “verifying shim sbat data failed” message. I now have to disable the secure boot.
It happens because I use “csh” as my shell, but “csh” (really “tcsh”) is not on the install DVD. So the normal desktop startup fails because of the lack of a shell, so there is a fallback to using “twm” for one window.
When that happens, I use “chsh” to change my shell to bash. I then logout and login again and all is fine. When I have installed “tcsh”, I can revert to my preferred shell.
I don’t know whether that is your specific problem, but perhaps it will at least give you a hint as to what might be wrong.
You can either, try again to perform the upgrade or, you can carefully use “mokutil” to get the SHIM certificates in place …
Please be aware that, the “Blue Screen” MokUtil uses when you reboot, expects a US-ASCII Keyboard –
Set the password MokUtil uses to something very simple «like 6 digits» – don’t worry about security – you’re the only one sitting at the keyboard when the system begins booting (after the Mainboard splash and before the openSUSE “choices” splash) …
Yo may also have to get into the certificates managed by your Mainboard to resolve this issue – the MOK certificates are usually not visible from the Mainboard’s UEFI/BIOS.
Yes, except OP did not provide any information allowing us to guess what happened. But booting Leap 15.4 ISO after Leap 15.5 would certainly trigger this problem.