Вытащил солюшен на уровень выше, чтобы прощё было дотнетить

BlazorWebAssemblyVisaApiClient/App.razor

@@ -0,0 +1,15 @@
+@using BlazorWebAssemblyVisaApiClient.ErrorHandling
+<GlobalErrorHandler >
+    <Router AppAssembly="@typeof(App).Assembly">
+        <Found Context="routeData">
+            <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)"/>
+            <FocusOnNavigate RouteData="@routeData" Selector="h1"/>
+        </Found>
+        <NotFound>
+            <PageTitle>Not found</PageTitle>
+            <LayoutView Layout="@typeof(MainLayout)">
+                <p role="alert">Sorry, there's nothing at this address.</p>
+            </LayoutView>
+        </NotFound>
+    </Router>
+</GlobalErrorHandler>