no conf file

[nezuko98123]

there is no lightdm-webkit2-greeter.conf file in /etc/lightdm/ directory instead there is web-greeter.yml file

[krzxsiek]

I have same problem on Debian 10 :(
lightdm and lightdm-gtk-greeter is installed

[JezerM]

You have installed web-greeter 3.0.0, not lightdm-webkit2-greeter. So no ".conf" file; instead, modify /etc/lightdm/web-greeter.yml.

Set theme to glorious and be sure to have the glorious theme inside /usr/share/web-greeter instead of /usr/share/lightdm-webkit.

If you wonder where to get lightdm-webkit2-greeter, there is no answer. You can install it through apt, but it won't work for sure. Just use web-greeter; it's the same. Also, check my fork :D