I created a Sample Blazor Server App with Azure Ad B2C by following this Documentation.

I successfully logged in and logged out without any issues.

Below is My Complete code.

Program.cs:

using System.Reflection;
using Microsoft.AspNetCore.Authentication.OpenIdConnect;
using Microsoft.Identity.Web;
using Microsoft.Identity.Web.UI;
using BlazorApp1.Components;
using System.Security.Claims;
namespace BlazorApp1;
public class Program
{
    public static void Main(string[] args)
    {
        var builder = WebApplication.CreateBuilder(args);
        var env = builder.Environment;
        builder.Configuration
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
            .AddEnvironmentVariables()
            .AddUserSecrets(Assembly.GetExecutingAssembly(), optional: true);
        builder.Services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
            .AddMicrosoftIdentityWebApp(builder.Configuration.GetSection("AzureAdB2C"));
        builder.Services.Configure<OpenIdConnectOptions>(OpenIdConnectDefaults.AuthenticationScheme, options =>
        {
            options.Events = new OpenIdConnectEvents
            {
                OnSignedOutCallbackRedirect = ctxt =>
                {
                    ctxt.Response.Redirect(ctxt.Options.SignedOutRedirectUri);
                    ctxt.HandleResponse();
                    return Task.CompletedTask;
                },
                OnTicketReceived = ctxt =>
                {
                    var claims = ctxt.Principal?.Claims.ToList();
                    return Task.CompletedTask;
                }
            };
        });
        builder.Services.AddControllersWithViews().AddMicrosoftIdentityUI();
        builder.Services.AddRazorComponents()
            .AddInteractiveServerComponents()
            .AddMicrosoftIdentityConsentHandler();
        builder.Services.AddCascadingAuthenticationState();
        builder.Services.AddHttpContextAccessor();
        var app = builder.Build();
        if (!app.Environment.IsDevelopment())
        {
            app.UseExceptionHandler("/Error");
            app.UseHsts();
        }
        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseRouting();
        app.UseAuthentication();
        app.UseAuthorization();
        app.MapControllers();
        app.UseAntiforgery();
        app.MapRazorComponents<App>()
            .AddInteractiveServerRenderMode();
        app.Run();
    }
}

MainLayout.razor:

@inherits LayoutComponentBase
<div class="page">
    <div class="sidebar">
        <NavMenu />
    </div>
    <main>
        <div class="top-row px-4">
            <AuthorizeView>
                <Authorized>
                    Hello @context.User.Identity?.Name!
                    <a href="MicrosoftIdentity/Account/SignOut">Log out</a>
                </Authorized>
                <NotAuthorized>
                    <a href="/MicrosoftIdentity/Account/SignIn">Sign in with your social account</a>
                </NotAuthorized>
            </AuthorizeView>
        </div>
        <article class="content px-4">
            @Body
        </article>
    </main>
</div>
<div id="blazor-error-ui">
    An unhandled error has occurred.
    <a href="" class="reload">Reload</a>
    <a class="dismiss"></a>
</div>

appsettings.json:

 "AzureAdB2C": {
   "Instance": "https://<DomainName>.b2clogin.com/tfp/",
   "ClientId": "<clientid>",
   "CallbackPath": "/signin-oidc",
   "Domain": "<DomainName>.onmicrosoft.com",
   "SignUpSignInPolicyId": "<PolicyName>",
   "ResetPasswordPolicyId": "",
   "EditProfilePolicyId": ""
 }

Make Sure to Add Redirect URL in the App registration as shown below:

Output: