In Mate 1.28.2, how can I remove the background image from the login screen?

Where do I find this UI?

I honestly don't know which greeter I have. How can I find it out?
It is probably that same LightDM gtk+ greeter as I mentioned:

$ dnf list *greeter*
Updating and loading repositories:
Repositories loaded.
Installed packages
lightdm-gtk-greeter-settings.noarch 1.2.2-25.fc41        <unknown>

Available packages
cosmic-greeter.x86_64               1.0.0~alpha.3-1.fc41 updates
kgreeter-plugins.x86_64             1:4.11.22-41.fc40    fedora
lightdm-autologin-greeter.noarch    1.0-21.fc41          fedora
slick-greeter.x86_64                2.0.6-1.fc41         fedora
slick-greeter-cinnamon.noarch       2.0.6-1.fc41         fedora
slick-greeter-mate.noarch           2.0.6-1.fc41         fedora

The forum kicked me out for the next 22 hours, so this goes into an edit:

Is greeter and lock screen the same thing?
I thought that greeter is that where I enter my credentials when first logging into the system, whereas the lock screen is that which takes my password after waking from sleep. I need to remove the background from the latter.

@ricmarques

The forum does not allow me to attach images either.
Anyhow, now the wait timer is at 21 hour:

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