How do you handle 404 pages in Blazor?

The NotFound template section in the App.razor can be used for handling 404 pages. The router shows this content if it hits a route that is not available, which is a 404 page.

<Router AppAssembly="@typeof(Program).Assembly">
    <Found Context="routeData">
        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
    </Found>
    <NotFound>
        <LayoutView Layout="@typeof(MainLayout)">
            <p>Handled 404 page</p>
        </LayoutView>
    </NotFound>
</Router>

Create a component Page/Error.razor to display the 404 content.

I would suggest you check the below link for better understanding:

https://docs.microsoft.com/en-us/aspnet/core/blazor/routing?view=aspnetcore-3.0#route-templates