libQt5Core.so.5: version `Qt_5.12' not found error

[anda_skoa]

I installed Qt 5.12.1 on Ubuntu 18.04.

Using the Qt installer?

/path/to/Qt/project: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.12' not found (required by /path/to/Qt/project)

This says that the program is trying to use the system Qt (installed from distribution packages).

I cannot figure out the problem since it was working fine until some time ago.

You might have always used the system Qt without realizing it and all was fine since it happened to be the same version.

If Ubuntu has moved to a different version now then this suddenly stopped working.

Make sure you are using the correct qmake to create the build files.
You might also have to set the LD_LIBRARY_PATH variable to point to your Qt installation

Cheers,
_