NotSupportedException: Alternate keys are not supported by the MongoDB EF Core Provider.

public class A : TrackableEntity<AId>
{		
  public A(AId id) : base(id) { }		
  public AT Typo { get; set; } // This causes the error
  public string T { get; set; } = string.Empty;
}
public record AId(Guid Value) : EntityId(Value);
public record AT(string Value); 

public class EventsDbContext(DbContextOptions<EventsDbContext> options) : BaseDbContext<EventsDbContext>(options)
{		
protected override void OnModelCreating(ModelBuilder modelBuilder)		{				
modelBuilder.Entity<A>()
  .HasKey(a => a.Id);

modelBuilder.Entity<A>()						             .Property(a => a.Id)						.HasConversion(a => a.Value, a => new AId(a))						.HasElementName("_id");

// Also without adding the property with the conversion, the error still occures				
modelBuilder.Entity<A>()						.Property(x => x.Typo)					
.HasConversion(type => type.Value, type => new AT(type))					.HasElementName("type");
				
modelBuilder.Entity<A>()						.Property(a => a.T)						.HasColumnName("t")						.HasMaxLength(100)						
.IsRequired();
				

base.OnModelCreating(modelBuilder);		
}}