Kubuntu 26.04 X11 black screen with wire mouse pointer and no session, just back to login screen

[tux fan]

After upgrading from 25.10 to 26.04, whenever I try to login to x11 with 26.04 I just get a black screen with a wire mouse pointer which hangs for a couple of minutes then it returns to the login screen.

I have tried everything to get it working even reinstalling the whole desktop with

sudo apt --purge autoremove kubuntu-desktop plasma-workspace plasma-session-x11 plasma-session-wayland
sudo apt install kubuntu-desktop plasma-workspace plasma-session-x11 plasma-session-wayland -y

But nothing is helping and when I come back from X11 to wayland all my panels, i.e. taskbars are gone, so I have to reboot the system to get wayland back to it's current state.

I need to test some issues I'm having with wayland and I know my system was working perfectly with X11 on 25.10, so need to get back to x11 for a comparison to help isolate the cause.

Also certain tools like lact just simply do not work with wayland, i.e. it cannot open a window and I do not pretend to understand why so please don't interrogate me over that.

Obviously all my drivers are up to date, etc.

EDIT: I forgot to mention that I have also tried adding a new test user to see if the problems are local to me or system wide and the issue does happen to the test user too.

Operating System: Kubuntu 26.04 LTS
KDE Plasma Version: 6.6.4
KDE Frameworks Version: 6.24.0
Qt Version: 6.10.2
Kernel Version: 7.0.0-22-generic (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 9800X3D 8-Core Processor
Memory: 64 GiB of RAM (60.2 GiB usable)
Graphics Processor 1: AMD Radeon RX 9070 XT
Graphics Processor 2: AMD Ryzen 7 9800X3D 8-Core Processor
Manufacturer: Micro-Star International Co., Ltd.
Product Name: MS-7E84
System Version: 1.0​

[Schwarzer Kater]

[…]
But nothing is helping and when I come back from X11 to wayland all my panels, i.e. taskbars are gone, so I have to reboot the system to get wayland back to it's current state.[…]

Unfortunately this can happen, I suppose because the X11 session is not officially supported anymore by the Kubuntu developers…
Also see the note for bonus step c. of Kubuntu 26.04 LTS - essential and advisable things to do directly after an installation.


Generally I would suggest creating a new user from a tty to test if the problems still persists…

[tux fan]

Generally I would suggest creating a new user from a tty to test if the problems still persists…

Oh sorry, I should have said I have already tried adding a new test user to see if the problem is me or system wide and it is the same black screen plus wire mouse pointer with the test user.
I'll edit my question to show that.

As for bonus step (c), plasma-session-x11 is already on the system, it's that which allows the x11 login option to be shown and I have reinstalled that when I reinstalled the desktop stack.

[Schwarzer Kater]

[…]
As for bonus step (c), plasma-session-x11 is already on the system, it's that which allows the x11 login option to be shown and I have reinstalled that when I reinstalled the desktop stack.

I suspected as much - I just meant the note.

And welcome to the forum, of course!

[tux fan]

And welcome to the forum, of course!

Thanks, hopefully someone can provide a solution because I've wasted almost 4 days on this so far and I'd really like to do a base comparison before taking extreme steps like bios changes and updates that may or may not solve some of my wayland issues.