This is the code that works for this question https://stackoverflow.com/questions/76786142/problem-running-a-ef-migration-from-a-docker-image-to-a-postgressql-server-from

PostgresConectionThatWorks.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using Npgsql;

namespace DockerPSQLGitHubActionDebug
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var services = new ServiceCollection();

            var connStringPostgresDb = "Host=myPostgreSQLServer.postgres.database.azure.com;Username=MyAdminUser;Password=LegalWorkingPassWord;Database=postgres;";
            PrintOtVaribles();

            TryConnectWithNpgql(connStringPostgresDb);

            var connStringTestDB = "Host=myPostgreSQLServer.postgres.database.azure.com;Username=MyAdminUser;Password=LegalWorkingPassWord;Database=testdb;";
            using MyContext context = await TryToRunMigration(services, connStringTestDB);
        }

        private static void PrintOtVaribles()
        {
            var SECRET_DEV_POSTGRESQL_ADMIN_LOGIN = Environment.GetEnvironmentVariable("SECRET_DEV_POSTGRESQL_ADMIN_LOGIN");
            var DB_PASENV_DEV_POSTGRESQL_ADMIN_LOGINSWORD = Environment.GetEnvironmentVariable("DB_PASENV_DEV_POSTGRESQL_ADMIN_LOGINSWORD");
            var SECRET_DEV_POSTGRESQL_ADMIN_PASSWORD = Environment.GetEnvironmentVariable("SECRET_DEV_POSTGRESQL_ADMIN_PASSWORD");
            var ENV_DEV_POSTGRESQL_ADMIN_PASSWORD = Environment.GetEnvironmentVariable("ENV_DEV_POSTGRESQL_ADMIN_PASSWORD");

            Console.WriteLine($"SECRET_DEV_POSTGRESQL_ADMIN_LOGIN: {SECRET_DEV_POSTGRESQL_ADMIN_LOGIN}");
            Console.WriteLine($"DB_PASENV_DEV_POSTGRESQL_ADMIN_LOGINSWORD: {DB_PASENV_DEV_POSTGRESQL_ADMIN_LOGINSWORD}");
            Console.WriteLine($"SECRET_DEV_POSTGRESQL_ADMIN_PASSWORD: {SECRET_DEV_POSTGRESQL_ADMIN_PASSWORD}");
            Console.WriteLine($"ENV_DEV_POSTGRESQL_ADMIN_PASSWORD: {ENV_DEV_POSTGRESQL_ADMIN_PASSWORD}");
        }

        private static async Task<MyContext> TryToRunMigration(ServiceCollection services, string connString)
        {
            //Configure DBContext with your connection string.
            services.AddDbContext<MyContext>(options => options.UseNpgsql(connString));

            //Building service provider
            var serviceProvider = services.BuildServiceProvider();
            var context = serviceProvider.GetRequiredService<MyContext>();

            try
            {
                //Running migration
                Console.WriteLine("Applying migrations...");
                await context.Database.MigrateAsync();

                Console.WriteLine("Migration test was successful!");
            }
            catch (Exception ex)
            {
                Console.WriteLine("Migration test failed!");
                Console.WriteLine($"Error: {ex.Message}");
            }

            return context;
        }

        private static void TryConnectWithNpgql(string connString)
        {
            try
            {
                using var conn = new NpgsqlConnection(connString);
                conn.Open(); // This will throw an exception if there's an issue connecting
                Console.WriteLine("Successfully connected to the database.");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Failed to connect to the database: {ex.Message}");
            }
        }
    }

}