Well, I should probably document my progress instead of hijacking someone else's thread.
Ref: Using Dark Theme On GDM and Lock Screen - #13 by mkjeller
For the Record, I am using Zorin 16 Pro, none of what I say below applies to Zorin Lite, Education or any releases prior to 16.
Like most of you here I found myself somewhat, irked, at the lack of customization GDM has for the login screen. Tools build to change the wallpaper don't work any more, or have weird side effects, and overall it's just a horrible janky mess.
Don't get me wrong, it's absolutely fine if you just want things to work out of the box, no issues with that at all! But as soon as you want to tweak it, it'll make your head spin!
Part 1: Switching to LightDM without compromising functionality
This is the bit that will probably interest most people.
Using a combination of lightdm and gnome-screensaver I managed to... kind of... replicate the gdm3 functionality. It's not as slick or clean, but I can customize it and it doesn't break!
This assumes you're the only user of the system and will only ever log into your main account.
sudo apt install -y lightdm gnome-screensaver- When prompted, make lightdm your DM of choice.
- Add
gnome-screensaverto your Startup Applications - Reboot
That's you, LightDM is now installed, and GNOME will automatically lock the screen based on the parameters in Settings -> Privacy -> Screen Lock
Super+L also works out of the box.
Woo hoo!
Part 2: Not using gnome-screensaver
In my travels I was introduced to a Google project.
xsecurelock
It's very simple, built with security in mind, and has some nice integrations with things like xscreensaver (boy did I miss some of those hacks).
But I encountered a problem. If I remove gnome-screensaver I lose screen blanking, automatic locking, and lock on system suspend. Super+L also stops working unless I manually create a shim in the keyboard shortcuts for it, but that doesn't resolve the other issues.
Incredibly the Zorin Menu (or whatever we call it, the analogue of the start menu) will call dm-tool lock when you click the Lock button (which invokes LightDM's lock window).
However, GNOME will not call any lock other than GDM3 or Gnome-Screensaver, and I'm at a bit of a loss on how to hack it together to get it to work right.
It's funny, if I'd been able to change my login screen wallpaper with no faff, I wouldn't have fallen down this rabbit hole!