adventure games with fixed scenes rarely would be ultra wide compatible as generally there is nothing extra to show with extra width. If more of a open world then it could perhaps but i think the demo it was fixed scenes wasnt it? Unless im mistaken. Was a while ago since i played the demo admittedly.

The Medium had almost the theme scnenario. Devs said that it was too difficult to remove blacks bars and add UW support in general. Just in one or two month they added it unless they say "it is almost impossible" or may take more time than you can imagine yourself =) . I hope that release vesion will have it otherwise i will have count on modders

There is a fix to add ultrawide support https://github.com/Lyall/SyberiaTWBFix and I can confirm it works even with the demo.
What I don't understand is why the developer is not supporting it from the start while some random internet person adds the support later with no issues...