SfSpreadsheet provides support to remove the outline’s label buttons by creating the custom OutlinesPanel and overriding the AddOutlineLabelButtons method like below.
Then you need to replace the default OutlinesPanel with this custom OutlinesPanelExt into the ControlTemplate of SfSpreadsheet. Please refer the App.xaml file of the attached sample.
The following screenshot illustrates the OutlinesPanel and Outline label buttons of SfSpreadsheet.
The following screenshot illustrates the SfSpreadsheet after removing the Outline label buttons.
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