Created attachment 160555 [details]
Config file producing the problem

SUMMARY
At some point when logging into my KDE system with X11, the desktop was empty: no symbols shown, despite files still being there in Dolphin.
It was also not possible to start most apps from the task bar: When clicking any of them, the regular square would appear around them (like when they're open) and it looks like it's loading, but after a few seconds that just disappears. I observed this behavior with: Dolphin, Firefox, Thunderbird, Signal Messenger, Discord. The only exception I found was Telegram Messenger, which started normally.
Starting apps from krunner or through a terminal worked just as usual. The issue did not occur when I logged in with Wayland instead.


STEPS TO REPRODUCE
1. Replace ~/.config/plasma-org.kde.plasma.desktop-appletsrc with the attached file
2. Re-log into KDE with X11
3. Desktop should be empty, starting apps from the task bar doesn't work (for most apps) 

OBSERVED RESULT
Desktop is empty, starting apps from the task bar doesn't work (for most apps) 

EXPECTED RESULT
Everything should be as usual: icons are on Desktop, apps can be started from taskbar

WORKAROUND
The problem seems to stem from ~/.config/plasma-org.kde.plasma.desktop-appletsrc. I've uploaded mine that produced the problem. It ends with the following section:
```
[ScreenMapping]
itemsOnDisabledScreens=
screenMapping=[...]
```
where [...] is a placeholder for a string of almost 2 million characters in length. Deleting this string, then re-logging into the system fixed the problem for me.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.108.0
Qt Version: 5.15.10
Kernel Version: 6.4.5-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 12 × AMD Ryzen 5 5600X 6-Core Processor
Memory: 31,3 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 1660/PCIe/SSE2
Manufacturer: Micro-Star International Co., Ltd
Product Name: MS-7C02
System Version: 3.0