First off...where all my multi-gpu whack jobs at? People with more sense than money!
Last few years I've watched things that have worked for 20+ years crumble into a giant mess. So I was hoping perhaps some others running Multi-XScreen/GPU here could toss in their two cents about what isn't trying to make our hardware trash.
Before moving to Garuda I tried all the "big" DE's in hope of finding refuge. Gnome, KDE, Mate, LXDE (or whatever the hell it is now), XFCE and maybe Enlightenment and Cinnamon. They're all busted. (good catch @Crispynut)
At present I have a semi working DE in a held back XFCE 4.12. The last XFCE that works. Though some of it was at the end of the 12 development cycle when they were already breaking things so it's not 100%. XFCE 4.14+ (last I checked) actually has the section where XScreens are enumerated commented out and forces/hard codes 1. " /* Previously, gdk_display_get_n_screens. Since Gtk 3.10, the number of screens is always 1. */"
Now if you're wondering what the issue is, well simply, it seems like every DE's WM, compositor and settings daemon is now broken with more than one XScreen. I'm guessing this is all some horrible conceptual pre-transition to Wayland. (no one has yet to refute this) Because of this I spent way too much time trying to work out an randr / Wayland style config. I eventually got randr working...ish. The performance is abysmal. GPU's sit at 50% idle, much less working in Blender or playing a game.
So if you're running Dual, Triple, Quad GPU how are you doing so and or what DE is playing nice with the XScreens if you are segregating by GPU? The key here is segregation. I could enable xine and call it a day...but then games would suck, I'd be fighting resolution issues constantly and I could not assign tasks/applications to specific GPU's.
Upon checking my posts on the XFCE forums I noticed some replies that the stupid site never notified me about. So I read, replied and went back to digging. Few other guys all with similar issues, same complaints but one dude mentioned this "break" was likely due to gtk. I found this interesting because under most DE to launch on another XScreen the syntax is DISPLAY=:0.1/0.2/0.3 (0 for the root...this used to be meaningful back in my BSD days) but under Gnome it's DISPLAY:1/2/3. However due to the gtk changes there is no longer an enumeration for XScreens. So gnome has a separate syntax for the thing it doesn't do anymore and it would seem also breaks anything else using gtk now.
Garuda is not a DE. Garuda is a distribution or "distro" and offers a wide variety of DE's which you named. You have offered no details about your system and the 4 GPU's and that makes it almost impossible for any of us "whack jobs" to help you.
I never said Garuda was a DE. I was before I moved to it I simply tried out a chit ton of DE's...on tons of different distros hoping someone had built a given DE in a way that works. I also said I was running XFCE on Garuda...why would I say that if I thought Garuda was my DE? ;p
The details of my system aren't relevant when I'm asking about others running multi XScreen/GPU and how they are doing it.