This forum is a great way to get in touch with RTG and bring issues to their attention. Morten, who responded here first, is RTG Staff.
He might be able to give you some better info, but probably not until Monday Oslo time.
That's great, thanks for your reply.
I worked out how to enforce the ultra wide resolution.
in ~/Library/Preferences/unity.Red Thread Games.Dreamfall Chapters.plist I have the following, and after editing I locked the file so the game cannot modify it.
Also, in Stream I set launch options to -screen-width 3440 -screen-height 1440
The game now runs on full resolution with occasional flicker, but that I can live with. Happy days