Use using for xmlns
MODIFY
WalletWasabi.Fluent/Views/NavBar/NavBarSearch.axaml
WalletWasabi.Fluent/Views/NavBar/NavBarSearch.axaml
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:conv="using:WalletWasabi.Fluent.Converters"
- xmlns:rx="clr-namespace:System.Reactive;assembly=System.Reactive"
- xmlns:i="clr-namespace:Avalonia.Xaml.Interactivity;assembly=Avalonia.Xaml.Interactivity"
- xmlns:ia="clr-namespace:Avalonia.Xaml.Interactions.Core;assembly=Avalonia.Xaml.Interactions"
+ xmlns:rx="using:System.Reactive"
+ xmlns:i="using:Avalonia.Xaml.Interactivity"
+ xmlns:ia="using:Avalonia.Xaml.Interactions.Core"
xmlns:vm="using:WalletWasabi.Fluent.ViewModels"
xmlns:search="using:WalletWasabi.Fluent.ViewModels.Search"
mc:Ignorable="d" d:DesignWidth="300" d:DesignHeight="80"

MODIFY
WalletWasabi.Fluent/Views/SearchPageView.axaml
WalletWasabi.Fluent/Views/SearchPageView.axaml
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
- xmlns:vm="clr-namespace:WalletWasabi.Fluent.ViewModels"
+ xmlns:vm="using:WalletWasabi.Fluent.ViewModels"
xmlns:search="using:WalletWasabi.Fluent.ViewModels.Search"
- xmlns:c="clr-namespace:WalletWasabi.Fluent.Controls"
- xmlns:conv="clr-namespace:WalletWasabi.Fluent.Converters"
- xmlns:i="clr-namespace:Avalonia.Xaml.Interactivity;assembly=Avalonia.Xaml.Interactivity"
- xmlns:behaviors="clr-namespace:WalletWasabi.Fluent.Behaviors"
+ xmlns:c="using:WalletWasabi.Fluent.Controls"
+ xmlns:conv="using:WalletWasabi.Fluent.Converters"
+ xmlns:i="using:Avalonia.Xaml.Interactivity"
+ xmlns:behaviors="using:WalletWasabi.Fluent.Behaviors"
mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
x:DataType="vm:SearchPageViewModel"
x:CompileBindings="True"

Use using for xmlns