This... actually... is what confuses me about resistance to LightDM.
I have never had LightDM glitch or fail me... Never had to reinstall it due to it suddenly being corrupted, as I had with GDM3 several times. Or an update mess it up, like GDM does.
It's configuration is easily set in just One File. It can use any system theme you want, any user theme... It can use a theme independent of the theme you normally use after logging in. Any background picture, any color, have a menubar or not have one... have a panel or not have one...
It can have any background image you want in the menubar - including it being opaque, translucent, transparent...
And most of the configuration can be set using a handy GUI with settings and buttons.
I've encountered exactly the same headaches with GDM3 as everyone else looking to customize it seems to have.
So I followed your advice, and tried out LightDM!
Logged in and immediately had Gnome complaining at me that I was no longer able to lock my computer because GDM wasn't my active Display Manager.
You got a workaround for that?
I have more experience with LightDM with other distros, and how Byzantine GDM customization is really ticks me off.
Open your keyboard settings and create the keyboard shortcut that is not the same as the GDM lockscreen shortcut. The command is xscreensaver-command -l
Turns out gnome-screensaver does that, and it all works out the box.
Couldn't get light-locker to work at all.
However gnome-screensaver only works on X. Not Wayland (which was what was tripping me up on a few things)
(Yeah, the shipped gnome-screensaver will segfault if you try and lock the screen under Wayland)
All I've got to figure out now is how to get gnome-screensaver daemon running without having it in my user autorun.
If you are using Wayland, that would explain the trouble. I can only recommend not using Wayland as it comes broken out of the box.
The concept behind Wayland is a good one. But it is incomplete. Many apps do not work with Wayland at all.
Yeah, I (personally) use X11 by default, plenty of apps hate Wayland.
Still exploring other options, but I have a fallback that I know works now
(LightDM, GDM and gnome-screensaver)
Gonna check out xsecurelock (by Google) and swaylock as well.
Love linux for this kind of thing, turns into a project that can keep you engaged.
I do wish that Zorin (or the GDM3 devs) would give us a nice configuration tool for their login screen though...
Update, xsecurelock is very nice and very basic (the way I like it), however GNOME is a pain in the rear-end when it comes to using not-gnome stuff.
So the system won't lock on wake from suspend and Super+L won't work unless I set a custom keybind.
Hilariously, calling dm-tool lock takes me back to the LightDM greeter (so I never needed gnome-screensaver in the first place), but GNOME doesn't usedm-tool lock it does it's own witchcraft to call either GDM3's lock or gnome-screensaver if the latter's daemon running.
Update 2
Wow... not using gnome-screensaver is a gigantic pain...
GNOME only wants to work with GNOME things. If I want to use light-locker, or xsecurelock or anything that isn't GDM or gnome-screensaver I have to sacrifice something. Like automatic locking on screen blank, or lock on resume from sleep.
Gnome devs, why can't I just tell gnome to use a specific command for locking things instead of having to try and hack something together?
Update 3 - an aside
Here's the hilarious thing.
If GDM3 just let me change my login screen wallpaper, I'd not have fallen down this rabbit hole.
Update 4
The lock button in the start menu... invokes lightdm...
but Super+L, Sleep and Screen Blank invoke some kind of dbus call.
Who designed this...
Update 5
Spun up my own thread because I technically hijacked this one, oops
I bumped the excellent write up to Tutorials and Guides in hopes it makes it more easy to find for others. In General Help, it will quickly get swamped and buried.