Hello to everybody, as I'm new to this forum and relatively new to KaOS. After the major update roughly one week ago, I encountered some graphics problem on boot-up I haven't managed to fix yet. At first, I thought it's similar to the one described here: https://forum.kaosx.us/d/2533-reboot-after-upgrade-no-sddm-only-black-screen-and-mouse-pointer. However, a few seconds after the black screen, some graphical elements like the KDE Wallet Manager do show up, but I can‘t actually access them (even the clock widget on my desktop freezes immediately). The login screen generally works, but after a while, it starts to "blink" (turn on and off) but is still responsive. According to systemctl status sddm.service, sddm is active (running). I've kept the system up to date via sudo pacman -Syu, but nothing has changed yet. Hardware data is listed here: https://paste.ee/p/BGTJl

Booting a KaOS live system from USB on this laptop only works if I take the 2020.05 ISO, which I had used for the initial install. With the 2020.07 ISO, there‘s just a black screen and a mouse pointer, plus the error message "Configuration file /var/lib/sddm/.config/sddm-greeterrc not writable. Please contact your system administrator." However, I can boot from the same 2020.07 ISO on my other laptop: https://paste.ee/p/kZ76G. I'd appreciate any help, thanks.

Not clear what you updated, since you hardware paste lists quite old versions of Plasma & inxi, kernel is from early May too, not what is current in core. Or is this paste from before you encountered issue, Live ISO?
To be able to help, for sure the pacman.log is needed (in live mode, go to /var/log/pacman.log from your installed system, not /var from the live session).
Since you mention the new ISO has issue too, this might be a kernel problem, to test that you will have to install the previous kernel, will link to that after confirming with the pacman.log you actually used linux 5.7.8.

Thanks for your reply. Yes, both hardware pastes are from live sessions, the first one is the version from early may, the second one is the current ISO. According to inxi -Fxz, kernel of the installed system is 5.7.8-1.

That said, the pacman.log is here. As you can see, I did quite a lot of trial&error based on some internet search results, including installing a driver for a graphic card my laptop doesn't even have. Though I've used several linux distros for years, I've only recently begun trying to understand at least the basics of how the OS works, plus this is my first KDE distro and the first one using pacman. So my learning curve is still pretty steep.

Log shows some dubious entries regarding installing from outside the KaOS repos......that is the best recipe to break the install.
But, for now let's hope you did not fully break it by doing that, and check if the kernel is not compatible with your hardware (there have been 2 reports now for KaOS were linux 5.7 is causing issues).
Install the previous kernel by booting up the system, once it hangs, go to tty2 (Ctrl-Alt-F2), login as your regular user, and run the following command (since the install is from May, I presume this kernel is not in your /var/cache/pacman/pkg cache):

sudo pacman -U https://sourceforge.net/projects/kaosx/files/packages/linux-5.6.8-1-x86_64.pkg.tar.zst https://sourceforge.net/projects/kaosx/files/packages/linux-headers-5.6.8-1-x86_64.pkg.tar.zst

and reboot (sudo reboot)

I did that, but there was an error stating - if my translation is correct - "failed to prepare transaction (could not satisfy dependencies): installing linux (5.6.8-1) breaks dependency 'linux>=5.7.7' required by tomoyo-tools" ("Fehler: Konnte den Vorgang nicht vorbereiten (Kann Abhängigkeiten nicht erfüllen): Installation von linux (5.6.8-1) verletzt Abhängigkeit 'linux>=5.7.7', benötigt von tomoyo-tools" in German). Situation after boot up remains the same.

Yes, I had installed some packages from the KCP, but uninstalled them as they didn't work anyway. The only exception is Zotero which hadn't caused any major problems, as far as I can tell.

If you don't need tomoyo (just used for hardening your system, but not done so by default), remove tomoyo, sudo pacman -R tomoyo-tools, then run the pacman -U line again (tomoyo is always rebuild on the latest kernel).

That helped a lot, thank you. There still are some minor issues that, as I remember, had already popped up now and then in the live system before the installation, but were gone after a while in the installed system. So I hope it'll work like that again. I guess I should update the kernel not before version 5.8 is out, then?

Not clear if downgrading the kernel fixed, but if it did, add linux & linux-headers to the ignore packages in your /etc/pacman.conf.
Then install linux-next:
https://kaosx.us/docs/kernels/
After you add that kernel, you can choose in your bootloader menu which kernel to start, try the linux-next kernel regularly, and please note here when linux-next is working again.
Linux-next is at 5.7.10 right now, so might already contain needed fixes, will move to 5.8RC7 tomorrow or so.
And it always is good to have 2 kernels to choose from, so even if all works, just keep linux-next around.

11 days later

Hello again. I've just tried out the 5.8.0-1-next kernel, but the problem persists.

6 months later

As suggested, I've tried the linux-next kernel regularly during the past months, and finally, the update to 5.10.9-1-next has solved the problem.