applies both to version in main repo and latest v.1.13.1 in repo:
https://download.opensuse.org/repositories/network/openSUSE_Leap_15.2/network.
repo

Error: Failed to start     "QtWebEngineWidgets could not be imported"

 # zypper se libqt5-qtwebengine

S | Name               | Summary                | Type
--+--------------------+------------------------+--------
i | libqt5-qtwebengine | Qt 5 WebEngine Library | package


After a brief research, I installed python3-qtwebengine-qt5
This way qutebrowser starts but only with QtWebKit backend, not with WebKit.

Note: Nouveau graphic drivers used