I've recently switched to Kubuntu 20.04. As I was adjusting the global themes, I noticed that switching to "Breeze Dark Theme" would make my lock screen go black, but switching to any other global theme restores the lock screen to display the default background image (which I haven't figured out how to change as changing the login screen or desktop backgrounds have no effect on the lock screen, or so I've noticed). I do not recall experiencing this problem the other day with this global theme, nor does it make any sense that changing the theme would effect the lock screen background image. Any ideas as to what's going on here and any solutions?

Actually, never mind. Although I don't know why changing the global theme changes the lock screen, I found the lock screen customization options under System Settings > Workspace Behavior > Screen Locking. This at least allows me to set the lock screen to whatever I want.