This lck file was meant to be locking the list of recent projects only. To be able to clear it completely, please navigate to Users/<user>/Library/Preferences/GRAPHISOFT/AC 24 xxxx, there you'll find 2 files "Recent Documents (Project).prf" and "Recent Documents (symbol).prf". Move these 2 files somewhere else (as a backup), and try to start Archicad again. The list of recent opened files will be clear, and it can start registering new files again.
Nevertheless, this could be a serious issue. I believe there was a problematic file that somehow messed up the startup dialog. Maybe the 2 files I mentioned above can tell the developers something, but I'm not quite sure. Please let me know if this helps with the issue, and then we can dive in deeper into what triggered the crash.
Looking forward to hearing from you!
Technical Support Engineer