I employ the following launcher:
Code:
[Desktop Entry]
Type=Application
Name=Sigil
Comment=ePUB file editor
TryExec=sigil
Exec=env QT_QUICK_BACKEND=software sigil %F
Icon=sigil
Categories=Office;
MimeType=application/epub+zip;
Path=
Terminal=false
StartupNotify=true
And not, the /usr/lib/sigil value has not been added to $PATH.