I see that 'Owned' types is listed as supported but perhaps only with table splitting? When I use an owned type that is in a separate table it doesn't appear to be working. Here is the code to configure the owned entity:

modelBuilder.Entity<DmTransaction>(entity =>
{
     entity.OwnsOne(x => x.APPayment, a =>
     {
          a.ToTable(nameof(APPaymentExt));
          a.HasForeignKey(f => f.Transaction);
     });
}