Struggling to recover the login window I was used to

[AppLEaDaY]

I come from Ubuntu Mate Focal.
I noticed with Ubuntu Mate 22.04 Arctica is the default greeter and packages lightdm-settings and slick-greeter are not installed.
So I installed lightdm-settings and, to replace Arctica, I used the procedure pointed here:

How to change lockscreen and login wallpaper with Arctica greeter?

Not sure how it goes in 21.10, but you can install LightDM back by following (which was written for previous release) link below:

This way I can easily set a background image using an interface ("Login Window" in Control Center), though the background in the password input boxes is white and I cannot tell why. It wasn't white before with Ubuntu Focal. In general I'm very inexperienced with this area of the operating system and I cannot even tell whether putting apart Arctica Greeter was really needed or not.

I'm momentarily lost, and disappointed too: I found the mentioned lost functionality very handy and now I have to struggle to have it back.

Thanks in advance!

Andrea