Hi,
I remember a report like this few week ago.
I think there is a problem with PKG build environment which need to be updated (Qt 5.8.0 currently), or at least recompiled from scratch with same components version (through Macport), to include compatibility with recent MacOs.
The problem come from Macports which break the compilation quickly due to packages which need to be updated in compilation rules. Macports is really a big puzzle.
As i don't yet installed MacOS 10.13.x for security reasons (i'm wait that Apple published a real stable release), i cannot check the problem on my Macbook pro.
To investigate, can you go to /opt/digikam/Applications/KF5/digikam.app/Contents/MacOS/ and run digiKam from a console.
Report here all debug trace printed while startup.
Thanks in advance
Gilles Caulier