Lock screen wallpaper option on Ubuntu 20.04 LTS is not available unlike in 18.04 LTS.
2 Answers
Ubuntu 20.04 uses the newest version of Gnome 3.36. This version has a new lock-screen now, it doesn't have separated screensaver and login window anymore but the same window for both. Also the new lock screen doesn't display any separated picture now - it blurs a wallpaper you have on your desktop (you can easily check it changing wallpapers and locking your screen). In other words, it's not a bug but absolutely normal behavior. I assume there is or there will be some possibility to change it, perhaps Dconf can help with that but I'm not sure since this is a pretty new feature.
2You can have a lock screen wallpaper as you wish with this extension.
