要在所有Identity页面上覆盖布局，可以按照以下步骤进行操作：

1. 创建一个自定义布局视图，用于覆盖Identity页面的布局。可以在Views/Shared文件夹下创建一个名为_LayoutIdentity.cshtml的文件，并在其中定义自己的布局样式。

    
    
    
    @RenderSection("Styles", required: false)


    

        
My Application
        
    
    

        @RenderBody()
    
    
    @RenderSection("Scripts", required: false)

2. 在Startup.cs文件中的ConfigureServices方法中，添加以下代码来指定使用自定义布局视图：

services.ConfigureApplicationCookie(options =>
{
    options.LoginPath = "/Identity/Account/Login";
    options.LogoutPath = "/Identity/Account/Logout";
    options.AccessDeniedPath = "/Identity/Account/AccessDenied";
    options.Events = new CookieAuthenticationEvents
    {
        OnRedirectToLogin = ctx =>
        {
            if (ctx.Request.Path.StartsWithSegments("/api") && ctx.Response.StatusCode == 200)
            {
                ctx.Response.StatusCode = 401;
            }
            else
            {
                ctx.Response.Redirect(ctx.RedirectUri);
            }
            return Task.CompletedTask;
        }
    };
    options.Cookie.Name = "YourAppCookieName";
    options.Cookie.HttpOnly = true;
    options.ExpireTimeSpan = TimeSpan.FromMinutes(60);
    options.SlidingExpiration = true;
});

services.AddMvc()
    .AddRazorPagesOptions(options =>
    {
        options.Conventions.AuthorizeFolder("/Account/Manage");
        options.Conventions.AuthorizePage("/Account/Logout");
    })
    .AddRazorPagesOptions(options =>
    {
        options.Conventions.AddAreaPageRoute("Identity", "/Account/Login", "/Account/Login");
        options.Conventions.AddAreaPageRoute("Identity", "/Account/Register", "/Account/Register");
    })
    .AddRazorPagesOptions(options =>
    {
        options.Conventions.ConfigureFilter(new IgnoreAntiforgeryTokenAttribute());
    })
    .AddRazorPagesOptions(options =>
    {
        options.Conventions.AddPageRoute("/Error", "{*url}");
    })
    .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
    .AddRazorRuntimeCompilation();

3. 在Views/Shared文件夹下，找到名为_ViewStart.cshtml的文件，将其内容更改为以下内容：

@{
    Layout = "_LayoutIdentity";
}

通过按照以上步骤操作，您将能够在所有Identity页面上使用自定义布局。