Bug 483734

SUMMARY
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Dolphin forgets default applications for file extensions outside of KDE environments, such as in awesomeWM, requiring re-assignment after each restart.
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### STEPS TO REPRODUCE
1. Set default applications for various file extensions in Dolphin. The apps are remembered and called correctly.
2. Restart PC.
3. Open Dolphin and try to open files with previously set default applications. Information is lost. Necessary to insert default app again...

### OBSERVED RESULT
Dolphin does not remember the set default applications for any file extensions and prompts for default application selection again. After a system restart, Dolphin still does not remember any default applications for file extensions.

### EXPECTED RESULT
Dolphin should remember the default applications for file extensions across different desktop environments and sessions, similar to its behavior within KDE Plasma 5 environments. This expected behavior indicates a potential issue with Dolphin's integration or use of `xdg-open` or similar mechanisms for handling default applications in non-KDE environments.

### SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.0.2
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.7.9-zen1-1-zen (64-bit)
Graphics Platform: X11
Processors: 12 × AMD Ryzen 5 3600 6-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 6700 XT
Manufacturer: Gigabyte Technology Co., Ltd.
Product Name: X570 AORUS ULTRA
System Version: -CF

### ADDITIONAL INFORMATION
This issue seems specific to Dolphin; other applications do not exhibit this problem and correctly remember their default application settings across sessions and different window managers. This might suggest a problem with how Dolphin interacts with the system's default application settings outside of KDE environments, possibly related to `xdg-open` or another mechanism Dolphin uses to manage default applications.