UGENE 1.31 on macOS was released with Qt 5.6.2.0 and Qt WebEngine. However, there was a critical issue with macOS Mojave (UTI-213).
So, UGENE 1.31.1 and 1.32 on macOS were released with Qt 5.4.2.0 and QtWebKit. We were not able to use a newer Qt version and Qt WebEngine because of various Qt-specific errors.
QtWebKit is obsolete. It is required to move to Qt WebEngine. This will be possible only when the issues will be fixed in Qt.
This epic lists issues that were detected in UGENE when it is built with Qt WebEngine and a newer Qt version.
See also a summary wiki page.