Hi Sascha,
Thanks for contacting Syncfusion support.
We have checked the reported query “To hide the closed button in the column chooser window" and you can achieve this by customize the style of column chooser and set visibility collapsed to the window closed button.
<syncfusion:TitleButton x:Name="CloseButton" Visibility="Collapsed"
Grid.Column="1"
Margin="0,5,2,10"
HorizontalAlignment="Right"
Command="syncfusion:ChromelessWindow.CloseWindow"
syncfusion:WindowChrome.IsHitTestVisibleInChrome="True"> |
We have attached the sample for your reference and you can download the same from the following link
Regards,
Jayaleshwari N