I mean, my data point of one isn't all that helpful if you're having issues, but triple monitors do indeed work on my end.

I switch between a station that has a 4k display next to a standard 1920x1080 display as well as my laptop display (3200x1800) and my home setup with the laptop and 2 4k displays.

I had an issue on the 4k displays when I attempted to run two displays and a usb hub on a single thunderbolt line, but that wasn't Wayland, that was me being dumb: The thunderbolt protocol only support 40Gb/s and each monitor uses 20Gb/s and the hub eats another 10Gb/s. If the hub got detected last, it dropped to usb 2, if one of the monitors came online last, it would drop to 30hz refresh rate. Frankly - I was a little floored when I realized that I was the one being dumb and the system was mostly still just making things work. Just for shits and giggles I booted up an x-session after to see what it does. The answer is lots of black screen.

I'm guessing that's an AMD GPU thing and not a Wayland thing. I run a triple-monitor setup with an AMD GPU on X.org and I have a similar problem: every once in a while when I boot my PC one of the monitors just doesn't come to life. Restarting X usually fixes it.

But the bootscreens work! X11 withmodesetting ddx works!

Moreover: when I pass through the dGPU to a virtualized macOS, all monitors I plug in just work!

>> Cannot say Wayland works smoothly on my triple-monitor setup.

How does X work on that setup?

Very smoothly.

Well until you need mixed scaling and then it completely falls down.

That’s why I have triple-4k monitor setup. Also good for the eyes.

Mixed scaling? Is that that thing when you open chrome and it’s blurry on your hidpi monitor?

To be fair, triple monitors barely work on my macbook