Any Patchnotes on what changed for 1.6?

How, today, can one update software without patchnotes...

We don't know, and patch notes have been pretty lackluster on GOG for years.

You mean this one?:
https://www.knightsandmerchants.net/information/the-peasants-rebellion/version-h

There has been a lot of things changed

in the new patch: multiplayer no longer works properly in winows 8.1. trying to join a multiplayer game instead crash the game. it is not possible to join, just host. in windows 10 however it crash after an hour. forcing a hard reset.