The large patch 1.6 including a new tutorial for Age of Wonders 3 is now available for Linux on Steam.

The developer advertised this in the Steam-Forum as follows:

Age of Wonders V1.6 launches, includes new Tutorial

Today we unleash Age of Wonders v1.6! This free update includes an overhaul to Random Maps, which now features greatly enhanced Underground experience. Other improvements include balance and interface fixes, enhanced AI, loading screen tips and a Tutorial for beginning players. V1.6 is available now on Steam!

The complete and very long Patch-Notes can be read here.