It might be a good idea for you to watch all the new feature clips for AC 16, 17 and 18. They should take a few hours only and get you up to speed on what changed.
Here:
you can find all the playlists on the ArchiCAD YouTube channel. Watch any playlist the name of which starts with "ArchiCAD 16 New Features" or "ArchiCAD 17 New Features" or "ArchiCAD 18 New Features".
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