Allow queries for mapped abstract base class with no discriminator

Start with the EF Core 5.0 model configuration and DbContext usage shown in the issue, then reproduce both SaveChanges and CountAsync with the supplied SQL Server setup. Done means determining the expected behavior for a mapped abstract base class without a discriminator and documenting or testing the confirmed failure.

Hi,
I am experiencing an issue while building model using EF Core (EF Core 5.0).
Console application (NET5) fails when trying to SaveChanges: "AMOS_ADDRESS is not mapped to a Table"
as reported in the attached screenshot.
Please can you help me in understanding what I am doing wrong?
Thanks

       var loggerFactory = LoggerFactory.Create(builder => {
            builder.AddFilter("Microsoft", LogLevel.Debug)
                   .AddFilter("System", LogLevel.Debug)
                   .AddFilter("ConsoleApp4.Program", LogLevel.Debug)
                   .AddConsole();
        });
        var optionBuilder = new DbContextOptionsBuilder();
        optionBuilder.UseLazyLoadingProxies(true);
        optionBuilder.UseLoggerFactory(loggerFactory);

        var modelBuilder = new ModelBuilder();
        modelBuilder.HasDefaultSchema("AMOS");
        modelBuilder.Entity<AMOS_ADDRESS>(b => b.ToTable("ADDRESS"));
        modelBuilder.Entity<AMOS_ADDRESS>().Property(e => e.CODE).HasColumnName("CODE");
        modelBuilder.Entity<AMOS_ADDRESS>().Property(e => e.ALPHACODE).HasColumnName("ALPHACODE");
        modelBuilder.Entity<AMOS_ADDRESS>().Property(e => e.ADDRESSID).HasColumnName("ADDRESSID");
        modelBuilder.Entity<AMOS_ADDRESS>().HasKey(e => e.ADDRESSID);

        modelBuilder.FinalizeModel();
        optionBuilder.UseModel(modelBuilder.Model);

        //optionBuilder.UseInMemoryDatabase(databaseName: "myDb");
        var connection = Microsoft.Data.SqlClient.SqlClientFactory.Instance.CreateConnection();
        connection.ConnectionString = "Data source=localhost;Initial catalog=ABS10.0.30;User ID=amos;Password=voyager";
        connection.Open(); // Works
        // To prove that table exists and connection works
        using (var command = connection.CreateCommand())
        {
            command.CommandText = "SELECT COUNT(1) from AMOS.ADDRESS";
            var count = (int)command.ExecuteScalar();
            Console.WriteLine($"Address count {count}");
        }
        optionBuilder.UseSqlServer(connection);

        var dbContext = new myDbContext(optionBuilder.Options);
        dbContext.Addresses.Add(new AMOS_ADDRESS() { CODE = "001", ADDRESSID = 1, ALPHACODE = "A001" });
        dbContext.Addresses.Add(new AMOS_ADDRESS() { CODE = "002", ADDRESSID = 2, ALPHACODE = "A002" });
        dbContext.Addresses.Add(new AMOS_ADDRESS() { CODE = "003", ADDRESSID = 3, ALPHACODE = "A003" });
        dbContext.Addresses.Add(new AMOS_ADDRESS() { CODE = "004", ADDRESSID = 4, ALPHACODE = "A004" });
        dbContext.SaveChanges(); // FAILS AMOS_ADDRESS is not mapped to a table

        var addresses = dbContext.Addresses;
        Console.WriteLine(addresses.CountAsync().Result); // Fails AMOS_ADDRESS is not mapped to a table