Bootstrap 5 Usage

1. NuGet packages

First step is to install a Bootstrap provider for Blazorise:
Install-Package Blazorise.Bootstrap5
You also need to install the icon package:
Install-Package Blazorise.Icons.FontAwesome

2. Source files

The next step is to change your index.html or _Host.cshtml file and include the CSS and JS source files:
<html>
<head>
  <!-- inside of head section -->
  <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-F3w7mX95PdgyTmZZMECAngseQB83DfGTowi0iMjiWaeVhAn4FJkqJByhZMI3AhiU" crossorigin="anonymous">
  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.15.4/css/all.css">

  <link href="_content/Blazorise/blazorise.css" rel="stylesheet" />
  <link href="_content/Blazorise.Bootstrap5/blazorise.bootstrap5.css" rel="stylesheet" />
</head>
<body>
  <div id="app"></div>

  <!-- inside of body section and after the div/app tag  -->
  <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.1/dist/js/bootstrap.bundle.min.js" integrity="sha384-/bQdsTh/da6pkI1MST/rWKFNjaCP5gBSY4sEBT38Q/9RBh9AH40zEOg7Hlq2THRZ" crossorigin="anonymous"></script>
</body>
</html>

3. Usings

In your main _Imports.razor add:
@using Blazorise

4. Registrations

Depending on the hosting model of your Blazor project you only need to apply either step 4.a or 4.b. You should not include both of them as that is generally not supported.

To Learn more about the different project types you can go to the official documentation.

This step is mandatory for Blazor WebAssembly (client-side). You should place the code into the Program.cs of your client project injecting the required Blazorise dependencies.
// other usings
using Blazorise;
using Blazorise.Bootstrap5;
using Blazorise.Icons.FontAwesome;

public class Program
{
  public static async Task Main( string[] args )
  {
    var builder = WebAssemblyHostBuilder.CreateDefault( args );

    builder.Services
      .AddBlazorise( options =>
      {
          options.ChangeTextOnKeyPress = true;
      } )
      .AddBootstrap5Providers()
      .AddFontAwesomeIcons();
    
    builder.Services.AddSingleton( new HttpClient
    {
      BaseAddress = new Uri( builder.HostEnvironment.BaseAddress )
    } );

    builder.RootComponents.Add<App>( "#app" );

    var host = builder.Build();

    await host.RunAsync();
  }
}
For Blazor Server project, or any regular ASP.NET Core hosted project types. You should place the code into the Startup.cs injecting the required Blazorise dependencies.
// other usings
using Blazorise;
using Blazorise.Bootstrap;
using Blazorise.Icons.FontAwesome;

public class Startup
{
  public void ConfigureServices( IServiceCollection services )
  {
    services
      .AddBlazorise( options =>
      {
        options.ChangeTextOnKeyPress = true; // optional
      } )
      .AddBootstrap5Providers()
      .AddFontAwesomeIcons();

    // other services
  }

  public void Configure( IComponentsApplicationBuilder app )
  {
    // other settings
    
    app.UseRouting();
    
    app.UseEndpoints( endpoints =>
    {
        endpoints.MapBlazorHub();
        endpoints.MapFallbackToPage( "/_Host" );
    } );
  }
}