Summary:

Installed Qt 5.15.2 and Qt Creator 4.14.0. Using Qt Creator to compile any code that requires Qt 5.15 causes error:

/usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.15' not found (required by /opt/Qt/5.15.2/gcc_64/lib/libQt5WebEngine.so.5)

Steps to reproduce:

1. Install Qt 5.15.2 in Linux using .run online installer with default path and basic installation. Not uninstalling default Qt version 5.12 from Ubuntu 20.04.
2. Run qtcreator.sh in /opt/Qt/Tools/QtCreator/bin so it sets the LD_LIBRARY_PATH and runs QtCreator
3. Load a project that requires Qt 5.15. (loading from a CMakeList.txt)
4. Configure project and set it to use Qt 5.15 located in the standard path: /opt/Qt/5.15.2/gcc_64/bin/qmake

1. Build and run the project. The build finishes and the progress bar gets green. However, the compiled program doesn't launch and the application output shows:

/usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.15' not found (required by /opt/Qt/5.15.2/gcc_64/lib/libQt5WebEngine.so.5)