use contentpresenter.
MODIFY
WalletWasabi.Fluent/Controls/QuestionControl.axaml
WalletWasabi.Fluent/Controls/QuestionControl.axaml
<Viewbox MaxHeight="150" DockPanel.Dock="Top">
<Image Height="100" Source="{TemplateBinding Icon}" />
</Viewbox>
- <ContentControl Content="{TemplateBinding Content}" DockPanel.Dock="Top"/>
+ <ContentPresenter Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}" DockPanel.Dock="Top"/>
</DockPanel>
</ControlTemplate>
</Setter>

use contentpresenter.