[Qgis-user] Not able to open qt designer after installing qgis via OSGeo4W

[Jochem Kail]

I installed QGIS and Qt designer using the OSGeo4W installer from the 
QGIS website (02.02.2026) via the express installation.
After installation, the Qt designer does not open via the desktop icon; 
it even gives no error message.
The QT Designer exe "designer.exe" is placed in "apps\qt5\bin". When I 
start the designer.exe here, some DLLs are missing: libpng16.dll, 
zlib.dll and more. They are located in "bin".
But after copying the missing dlls to "apps\qt5\bin" a new issue occurs: 
"This application failed to start because no Qt platform plugin could be 
initialized."
I am also not able to open Qt designer via the qgis-ltr-designer.bat.
I'm running QGIS 3.40.14 on Windows 11.