I don’t know if this is well known - but I know it from experience.
I have been able to run a Samsung Odyssey NEO G9 240Hz and Acer 144Hz display at the same time but only after buying high quality display port cables cable of running 144Hz. HDMI although also high quality was not enough. (Intel CPU and AMD WX7100 PRO)
My system is different now with a Lenovo P620 Workstation and RX 7900XTX and only the Odyssey display.
If that for any reason is not an option I can only offer speculation
Connection is often the weak link
connection cable must be of high quality
This is one may not be relevant as it relates to kwin
Windows does not equal Linux - and does not always support the same setup - that is just how it is and you cannot assume that Linux will work the way you intend.
And Linux is more self serviced - but as I said only speculations.
What happens if you set the laptop display at 60Hz?
However I do think Plasma on Wayland provides better support with AMD hardware.
On some personal experience - my past experience with AMD dates back 20y - and that was not great.
I thought if Lenovo builds a workstation like the P620 - it can’t go wrong - and I got hooked on AMD and just yesterday I got a new Lenovo X13 with AMD 7940U added to the collection (no OS so I am starting from scratch). I am looking forward to experience this from ground up.
Linux is much about finding the right configuration - and in doing so - sometimes requires a great deal of searching - reading - refine search - reading more - and suddenly - bam - there it is - a user having almost the same issue and while that user’s solution do not work in this case it hints you to the tweaking point.
Almost like tuning engines - there is a lot of adjustment options - which one is the right one to push that extra mile?
The link from above about color depth - refers to a kernel limitation - one should speculate the 6.8 perhaps even 6.9rc provides improvements in that regard.
I presume you tried KDE by performing a fresh install of the Manjaro KDE distribution, right? If you installed the KDE Display Environment on top of your existing XFCE, then that could produce unpredictable results.
Another plus for KDE is that Wayland is now the default DE; and you are able to switch between Wayland or X11 at the login screen.
It would be interesting to know if similar issues persist for you in both Wayland and X11, or whether its limited to only one of these.
That sounds like another issue entirely. There are (Manjaro-specific) tutorials for installing Nvidia drivers properly; you just need to search for them. I don’t use Nvidia (never will) so I don’t keep any links handy.
