Update seems o.k. - no error messages, reboot… then blackscreen.
Try to boot older kernel, same issue. Terminal session with Ctrl-Alt-F2 not possible… black is black 
Next I will try to go back with livestick and timeshift - hopefully - it is first time for me.
Perhaps NVIDIA error (GTX 1080)?
System 2 with AMD-GPU (Ryzen 4650G) update seems without problems (nearly same config and apps).
Michael
Oh, I see @philm above… 4k not mine, but 3840x1600 and DP. Perhaps here is Screen-Output on HDMI?
What is to do?