Sergeileduc After login, I see my wallpaper for 1-2 seconds, then black...
Yeah, same here, when I updated Plasma on my main workstation. When it failed, I rebooted, and when it came time to select the version to run, I took the second choice, and that worked. I didn't even notice which version I ended up running, but I don't use the Plasma edition normally, so it wasn't critical for now.
I just update my Plasma SSD when I update our Budgie and Mate machines, so I can see how its development is coming along.