After installing debian10, I always wanted to beautify the installed xfce4. But when I set to the lock screen of xfce4, I found that the system does not have corresponding settings to modify the lock screen of xfce4. So I kept searching on Google. Finally found a solution. it's actually really easy. Use the command to install lightdm-gtk-greeter-settings. Then on the system interface, you can find the setting tool to modify the lock screen interface
sudo apt-get install lightdm-gtk-greeter-settings