Created attachment 183437 [details]
Output from launching kdiff3 from WinDbg

SUMMARY
kdiff3 crashes on startup when installed as "Install for anyone using this computer"
When installed as "Install just for me" it works as expected

When starting from WinDbg halts with the following error:

Cannot mix incompatible Qt library (6.8.3) with this library (6.8.1)
(5d0c.5cf4): Security check failure or stack buffer overrun - code c0000409 (!!! second chance !!!)
Subcode: 0x7 FAST_FAIL_FATAL_APP_EXIT 
Qt6Core!QXmlStreamWriter::writeTextElement+0xb8:
00007ffe`f4786f08 cd29            int     29h

This happens on two different machines (both current Windows 11 Version 24H2 (x86_64)

STEPS TO REPRODUCE
1. Run kdiff3-1.12.3-windows-x86_64.exe
2. Choose "Install for anyone using this computer" and finish install
3. Start->kdiff3

OBSERVED RESULT
No UI appears.
When launched via WinDbg the attached information is generated prior to the crash.

EXPECTED RESULT
The program UI appears and the program runs as expected.
NOTE: if the program is installed as "Install just for me" it works as expected

SOFTWARE/OS VERSIONS
Windows:  Windows 11 Version 24H2 (x86_64)
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
I have both Visual Studio Code and Visual Studio 2022 community edition installed on both machines.