If the Expander.IsEnabled=false then the tooltip on the header is not active.
Is there a way to have a ToolTip even if Expander.IsEnabled=false?
<Expander.Header>
<TextBlock Text="Export" ToolTip="ToolTip - I don't show up if Expander.IsEnabled=false"
Style="{StaticResource TabItemHeaderSemiBold11}"/>
</Expander.Header>