Hello,
I've recently upgraded my OS to Mojave (OS X 10.14.4), and I've started having issues while opening DWG/DXF files.
My Archicad 19 (full license, USA version, build #9001, platform Mactel64) is supposedly up to date. However, when I now try to open or import a DWG or DXF file, AC systematically crashes.
I'm actually using AC19 on Mojave and if you stick to Archicad files, it works pretty well.
The issue I'm running into is limited to opening/importing DWG/DXF files. Ever since I upgraded to Mojave, AC19 crashes while trying to open this kind of files.
As Scott said, AC 19 is not supported for Mojave. So, if you have crashes, your only options are to downgrade your OS, boot from a bootable High Sierra clone (which you made before upgrading to Mojave, right?), run a virtual machine that has an earlier MacOS via Parallels Desktop etc (with associated performance hit), or pay to upgrade to AC 21 or 22...
A messy workaround may be to import PDFs of the drawings. Depending on how they are created you may be able to explode them into accessible linework to do what you need. On the other hand this may crash as well...
Apple iMac Intel i9 / macOS Sonoma / AC27UKI (most recent builds.. if they work)