SwaggerDefaultValues.cs

using Microsoft.AspNetCore.Mvc.ApiExplorer;
using Microsoft.OpenApi.Any;
using Microsoft.OpenApi.Models;
using Swashbuckle.AspNetCore.SwaggerGen;

namespace autogenerate_proto
{
    public class SwaggerDefaultValues : IOperationFilter
    {
        public void Apply(OpenApiOperation operation, OperationFilterContext context)
        {
            var apiDescription = context.ApiDescription;

            operation.Deprecated |= apiDescription.IsDeprecated();

            if (operation.Parameters == null)
            {
                return;
            }

            foreach (var parameter in operation.Parameters)
            {
                var description = apiDescription.ParameterDescriptions.First(p => p.Name == parameter.Name);

                if (parameter.Description is null)
                {
                    parameter.Description = description.ModelMetadata?.Description;
                }

                if (parameter.Schema.Default is null && description.DefaultValue is not null)
                {
                    parameter.Schema.Default = new OpenApiString(description.DefaultValue.ToString());
                }

                parameter.Required |= description.IsRequired;
            }
        }
    }
}