Seen the solution on another forum and works for me
you have the AI pack v3 by HALYCON installed.
This pack got an update tonight/ yesterday (here on steam) which had broken OMSI completely.
Do the following, as a workaround:
In the folder:
(..):\Steam\SteamApps\common\OMSI 2\RegAddons
you'll find a file called "Vol3KIMenschen_xxxxx".ini ,since todays update.
Just delete the "Vol3KIMenschen_xxxxx".ini" in that folder and OMSI will start again as usual.