So, I updated Tumbleweed, and the updates to KDE caused my Plasma/Wayland session to restart, breaking the updates part way through. I wasn’t watching at the time so took some while to debug!
Spent some time learning how to use nm-cli, because new half-upgraded KDE wouldn’t load the network widget. It looks like something else may have changed and mucked up in the half-update (and of course I rebooted like a wise-man/dummy/i-dont-know-but-at-least-it-didnt-make-it-work) but iterations of trying things in nmcli eventually worked!
Finally tried zypper dup again and saw the session restart, so finished the job from the virtual terminal! At last, I seem to have a working computer again, and I might just brave updating my main laptop. (I cancelled the update while it was still downloading packages, after seeing the breakage on the other laptop!)
I had more or less the same problem in my laptop and in my main PC. But you can get around it just by login again and doing the update through zypper. I believe it restarts the session 3 times, and one of those after login, you just have a black screen. Use Ctrl+Alt+T to bring up the terminal and zypper dup again. After zypper is done just restart and everything will be fine.
Did this with both PCs and both are working with no problems.
Yeah, if I’d known what was going on I could have just switched to VT1 straight away and finished the update. Did the other machine fine by updating from VT1 from the start.