If you’re still using the 340 nvidia driver (as mentioned in your profile) and you ran Plasma 6 which defaults to Wayland, I think this may be the source of your problem. Did you try X11 session?
Furthermore, I am not experiencing any show stopper bugs with KDE/Plasma 6, just a few minor annoyances, certainly nothing to severe enough to remain on KDE/Plasma 5. I didn’t seem to have the issues you or @radar have had.
I am using the nouveau driver. No, I did not try the X11 session.
did i get that correctly, that you tried out arch? And have no idea how manjaro has or has not improved upon it?
No problems with plasma 6 here …
And pretty much everyone else that has tried it seems to be OK too.
(but those were mostly capable Unstable users who got it in the proper way…)
@radar
thanks for your infos. i already expected that this transition to plasma 6 will bring up a lot of problems and i’m sure it will last the upcoming months (if not the whole year) till it runs in an acceptable way. i was scared from the first time because the kde-developers were sooo euphoric and every time something sounds to good to be truth then it isn’t truth. there are too much construction-sites with it: the step to wayland (fully ignoring all nvidia-users), the application-developers who have to modify/test/verify their applications for full funtionality to qt6, the distro-packagers who have to repack the repositories. it remembers me to the transition of kde4 to kde5/plasma. i’ll try to stand at plasma5 as long as possible and i’m already thinking to switch to another gui (xfce,cinnamon or something else) until this plasma6 doesn’t fear me as it does right now.
Its only a default … so it doesnt really present a barrier.
Also … nvidia that is not legacy works with wayland now.
Also … its really the fault of nvidia, not the other way around.
(as with all things in the opensource world where something is ‘not supported’ due to proprietary bs)
OK, I will now take me exit from this wild world of speculation.
And enjoy my plasma 6 with wayland.
(even my ‘papirus icons’ and ‘simple application launcher’ widget got updated for 6, woohoo)
Like I said in another post, the only issue I noticed with nvidia/Wayland, was the flickering with Vivaldi, everything else seems to work okay. That said, I did switch back to X11, no big deal.
Perhaps those with much customization will feel more pain when upgrading, but that can mostly be avoided by restoring to defaults like selecting Breeze before proceeding. I think your fear is a bit overblown, and I doubt anyone needs to switch to another GUI (this isn’t anything like the switch from KDE3 to KDE4)
Oh hey, it’s 
GNOME with Arc Menu and Dash to Panel. 
The Cube you will only draw with four virtual desktops.
Might be a triangle and the penta-gon with 3 or 5 as well.
Also the desktop effect must be activated, it’s not there by default.
Yes, I am one of those with a lot of customization. I use a LOT of configurable window buttons for example. I assume a lot of my problems are due to that and those buttons will need to be modded to KDE 6. I also use xrandr, which does not work in Wayland. But I need it to configure gamma on my dual monitor setup.
I’m planning to set up x11 as a default in Manjaro for some time. Using wayland and there are some issues on both Nvidia and non Nvidia cards
Like what?
From the samplings here it seemed some folks experienced more bugs on x11, but I may be conflating that with ‘missing features’ such as the recording option in spectacle (that requires wayland).
I ask out of genuine curiosity … I had been using x11 until this release.
If you’re interested, you can read the issues I’ve had with nvidia/wayland/Plasma6 - https://forum.manjaro.org/t/kde-megarelease-6-plasma-6-is-here/157389/101
That said, besides the browsers thing, everything else seems alright but I don’t use the Wayland session much since the flickering/tearing in the browsers is often unbearable.
I’m getting weird issues with windows geometry from time to time using different cards so assume it’s not GPU-related
And for nvidia there’s this
I may confirm the issue mentioned in your post
I’ve also tested with no problems opening *.webp files via Dolphin on the most recent fedora 40 KDE nightly build and on openSUSE Tumbleweed with sudo zypper dup as of today (03/23/24). CachyOS 2024.3 (with sudo pacman -Syu also as of today) showed up failure to open via Dolphin *.webp images.
Is what I just saw I accidentally installed (with their screenshotter with pamac) and I now have 4 Gnome login options. Bad idea to keep it next to Plasma?
There is absolute no reason to be sorry for using Plasma 6.
Of course if you are relying on third-party extensions - then you will be sorry - otherwise not.
I have been testing Plasma 6 since many moons - earlier than the official release - quite pleasant in my opinion.
But if its only affecting you I might think its configuration related.
To be fair, I have no idea if you included testing vanilla configs or not.
Just its the only report of that I know about.
Flickering with xwayland on nvidia does seem to be a thing.
(and makes me wonder also if @ydar tried making sure to run the browsers in native wayland?)
I’ve seen absolutely no issues with vsync on either xwayland or natively, with Firefox …? In fact, since switching to Wayland several months ago, all has been fine and certainly far better than an Xorg session? 
No NVIDIA here, in my case, though?
It’s reproducible under some very specific circumstances and actually minor.
And that’s pretty much the reason I don’t want to enable wayland by default for everyone. Also some remote desktop software doesn’t support Wayland (e.g. AnyDesk). I don’t really think it’s a good idea to break these kind of things.