Hi Krzysztof,
We have already logged the NewButton-related issue in the docking manager. We will include the fix in our upcoming Weekly NuGet release which is scheduled on 7th February 2023.
You can track the status of this defect using the following feedback link:
NewButton is not visible on Document window in WPF | Feedback Portal (syncfusion.com)
If you have any more specification replication procedures or a scenario to be tested, you can add it as a comment in the portal.
Please let us know if you need any further assistance.
Note: The provided feedback link is private, and you need to log in to view this feedback.
Regards,
Harinath N