Custom configuration provider value not mapped in stratup class's services.configure method in .NET core 3.1

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ASP.NET-Core

I am adding a Custom configuration provider in ConfigureWebHostDefaults and application configuration from Database.

What I have tried:

Host.CreateDefaultBuilder(args)               
                    .ConfigureWebHostDefaults(webBuilder =>
                    {
                        webBuilder.ConfigureAppConfiguration(AddDbConfiguration);
                        webBuilder.UseStartup<Startup>();
                    })

then add in IServiceCollection

services.Configure<List<SysAppConfig>>(Configuration.GetSection("AppConfig"));

but when I checking values in Configure method

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IOptionsMonitor<List<DTO_SysAppConfig>> optionsAccessor)
        {

            var option1 = optionsAccessor.CurrentValue.Count;

.......
}

Its showing count=0 .

please suggest me how to get values from Custom configuration provider and add in option for further use.