You can have your web browser opened, and your terminal only, this has nothing to do with your issue. Give your pacman log for this last update to see what went wrong. Did you accept all the replacement Pacman probably asked you, from all the Breath theme things? And yes I second what has been said in the other thread (right? that’s what you’re referring to I suppose), most issues are because of people not managing properly their system, holding updates for long time, not reading the current issues and solutions in the update announcement threads, things like that, and regarding this issue you had, I think that’s exactly your case, previous Stable update, they replaced Breath theme, there is also an issue/solution exactly about that:
SDDM shows wrong/default theme
Solution:
Set SDDM theme to Breath in System Settings / Startup and Shutdown / Login Screen (SDDM).