Qt5 programs do not work

What I have done so far: I’ve just installed FuryBSD, so my system is a FreeBSD 12.1. My configure script installed all programs and lib with pkg, so no port is involved.
Now when I try to start qtcreator, I get an error ‘Cannot mix incompatible Qt library (0x50d02) with this library (0x50e02)’.
Creator is a bad example, as it has its own versioning, but assistant got the same error. qt5-assistant is installed as 5.14.2, qt5-core is installed as 5.14.2_3.
Checking all dependencies of linguist, which uses less qt libraries: they all have 5.14.2. I do not understand why those programs do not run?

nextcloud does not run either, but core dumps directly. Any hint?

What may could be a problem: I’ve installed the subpackages of QT5, too, because some of them were missing last time (such as qt5-svg ot qt5-sensors). I want to be able to use them in my own programs in the future.

This sounds like a packaging bug unfortunately, please contact the FuryBSD community. There’s nothing we can do from here, they are mixing (or you mixed) incompatible Qt versions which isn’t supported.