The issue appears to be infinite recursion:

#0  0x00007f5ac3e2855a in scratch_buffer_init (buffer=<optimized out>) at ../include/scratch_buffer.h:77
#1  __GI___realpath (name=0x563cef8324b0 "/home/scarf/.local/share/plasma/look-and-feel/org.kde.breeze.desktop", resolved=0x7fffb31fac50 '\376' <repeats 200 times>...) at canonicalize.c:429
#2  0x00007f5ac46a906f in realpath (__name=<optimized out>, __resolved=0x7fffb31fac50 '\376' <repeats 200 times>...) at /usr/include/bits/stdlib.h:55
#3  QFileSystemEngine::canonicalName (entry=..., data=...) at /usr/src/debug/qt6-qtbase-6.8.2-3.fc41.x86_64/src/corelib/io/qfilesystemengine_unix.cpp:675
#4  0x00007f5ac44864f3 in QDir::canonicalPath (this=this@entry=0x7fffb31fbd58) at /usr/src/debug/qt6-qtbase-6.8.2-3.fc41.x86_64/src/corelib/io/qdir.cpp:702
#5  0x00007f5ac71754c7 in KPackage::Package::setPath (this=this@entry=0x7fffb31fbed0, path=...) at /usr/src/debug/kf6-kpackage-6.12.0-1.fc41.x86_64/src/kpackage/package.cpp:516
#6  0x00007f5aac12bf0f in LookAndFeelPackage::initPackage (this=<optimized out>, package=0x7fffb31fbed0) at /usr/src/debug/plasma-workspace-6.3.4-2.fc41.x86_64/shell/packageplugins/lookandfeel/lookandfeel.cpp:54
#7  0x00007f5ac71751ba in KPackage::PackageLoader::loadPackage (this=this@entry=0x563ccc487e20, packageFormat=..., packagePath=...) at /usr/src/debug/kf6-kpackage-6.12.0-1.fc41.x86_64/src/kpackage/packageloader.cpp:58
#8  0x00007f5aac12c499 in LookAndFeelPackage::pathChanged (this=<optimized out>, package=0x7fffb31fc170) at /usr/src/debug/plasma-workspace-6.3.4-2.fc41.x86_64/shell/packageplugins/lookandfeel/lookandfeel.cpp:60
#9  0x00007f5ac7175a65 in KPackage::Package::setPath (this=this@entry=0x7fffb31fc170, path=...) at /usr/src/debug/kf6-kpackage-6.12.0-1.fc41.x86_64/src/kpackage/package.cpp:529
#10 0x00007f5aac12bf0f in LookAndFeelPackage::initPackage (this=<optimized out>, package=0x7fffb31fc170) at /usr/src/debug/plasma-workspace-6.3.4-2.fc41.x86_64/shell/packageplugins/lookandfeel/lookandfeel.cpp:54
#11 0x00007f5ac71751ba in KPackage::PackageLoader::loadPackage (this=this@entry=0x563ccc487e20, packageFormat=..., packagePath=...) at /usr/src/debug/kf6-kpackage-6.12.0-1.fc41.x86_64/src/kpackage/packageloader.cpp:58
#12 0x00007f5aac12c499 in LookAndFeelPackage::pathChanged (this=<optimized out>, package=0x7fffb31fc410) at /usr/src/debug/plasma-workspace-6.3.4-2.fc41.x86_64/shell/packageplugins/lookandfeel/lookandfeel.cpp:60
#13 0x00007f5ac7175a65 in KPackage::Package::setPath (this=this@entry=0x7fffb31fc410, path=...) at /usr/src/debug/kf6-kpackage-6.12.0-1.fc41.x86_64/src/kpackage/package.cpp:529
#14 0x00007f5aac12bf0f in LookAndFeelPackage::initPackage (this=<optimized out>, package=0x7fffb31fc410) at /usr/src/debug/plasma-workspace-6.3.4-2.fc41.x86_64/shell/packageplugins/lookandfeel/lookandfeel.cpp:54


In this past, this has been caused by things like two themes falling back to each other.

FWIW I'm using Fedora 41 KDE myself, and I can't reproduce this issue when I log into the distro-provided session in a new user account.

Are you absolutely sure it's actually a new clean user account? The fact that you say it happens on Ubuntu too and persists after switching distros makes me think the issue is triggered by some bit of configuration that you brought along with you from Ubuntu to Fedora.

(In reply to Nate Graham from comment #2)
> FWIW I'm using Fedora 41 KDE myself, and I can't reproduce this issue when I
> log into the distro-provided session in a new user account.
> 
> Are you absolutely sure it's actually a new clean user account? The fact
> that you say it happens on Ubuntu too and persists after switching distros
> makes me think the issue is triggered by some bit of configuration that you
> brought along with you from Ubuntu to Fedora.

to be fair, i've only rm'd ~/.config/plasmashellrc and ~/.config/plasma-org.kde.plasma.desktop-appletsrc. i'd also like to reset KDE configuration but the KDE configs not in same namespace (~/.config/kde6/*) is making it hard, tho. i'm hesitant on removing the entirity of .config, but will check way to delete other KDE configs too.

i've removed everything named plasma in ~/.config, and now when i log in i immediately gets logged out.

Sounds like this is not really a clean installation since there is some amount of config data pulled over.

Can you try again in a new user account *with no files or config data copied over* and see if it still happens?

If it does not, then it's caused by something in your existing config data, and we'll need to find out what it is.

(In reply to Nate Graham from comment #5)
> Sounds like this is not really a clean installation since there is some
> amount of config data pulled over.
> 
> Can you try again in a new user account *with no files or config data copied
> over* and see if it still happens?

yes, a clean user installation works. 

> If it does not, then it's caused by something in your existing config data,
> and we'll need to find out what it is.

the problem is, even after I `rm -rf $HOME/.config`, I'm unable to even log in into my original graphical account. I just get immediately logged out upon logging, even after rebooting. `journalctl --user -xeu plasma-plasmashell.service` shows me nothing.

Sounds like a clean user account is actually fine, and the problem comes from something in your migrated user data. I suspect something in ~/.local/share/plasma.

If you can figure out what it is, that would be very useful.

(In reply to Nate Graham from comment #7)
> Sounds like a clean user account is actually fine, and the problem comes
> from something in your migrated user data. I suspect something in
> ~/.local/share/plasma.
> 
> If you can figure out what it is, that would be very useful.

found out the culprit, it was ~/.local/share/lookandfeel. I think it has to do with my custom KDE 5 theme (https://maribel.dev/kde/kde5-lockscreen.html) crashing after migrating to KDE 6.

Created attachment 180129 [details]
gzipped `~/.local/share/plasma/look-and-feel` package

also the look-and-file theme in question:

Yeah that's gonna account for it. Your theme claims it's Breeze, which has confused the system quite terribly. This is a theme configuration issue.