✅ EF Core 8.0.3 Many To Many Relation

[PrimaryKey(nameof(Id), nameof(SecondId))]
public class A
{
  public string Id { get; set; }
  public string SecondId { get; set; }

  public virtual ICollection<B> Bs;

  public A()
  {
    Bs = new HashSet<B>();
  }
}

public class B
{
  [Key]
  public string Id { get; set; }

  public virtual ICollection<A> As;

  public B()
  {
    As = new HashSet<A>();
  }
}

b.As.Add(new A());