Set PART_Popup style
MODIFY
WalletWasabi.Fluent/Views/NavBar/NavBar.axaml
WalletWasabi.Fluent/Views/NavBar/NavBar.axaml
<Style Selector="AutoCompleteBox /template/ ListBox#PART_SelectingItemsControl">
<Setter Property="Margin" Value="0" />
</Style>
+ <Style Selector="AutoCompleteBox /template/ Popup#PART_Popup">
+ <Setter Property="MaxWidth" Value="{Binding $parent[UserControl].Bounds.Width}" />
+ <Setter Property="PlacementGravity" Value="Top" />
+ </Style>
<Style Selector="AutoCompleteBox /template/ TextBox DataValidationErrors">
<Setter Property="IsVisible" Value="False" />
</Style>

Set PART_Popup style