@SFaulken Well... I updated again, and was only greeted by a terminal after reboot (as happened after the first try, but not the second). It was flickering a couple of times, which might have been SDDM failing to start I guess. Logged in with my regular account and ran startplasma-wayland, and once in there everything looked fine! Nothing missing, theme was ok. But SDDM failed on every boot. I reinstalled Tumbleweed, on the whole disk this time, and now I get "operating system not found" lol.