The target milestone is not is the link.
You can add a milestone in the links, but then it is just a Milestone, not a Target Milestone.

Thanks for your reply.
None of these works for a productVersion in the link items (added manually as a link)
[link_ProductVersion.idMilestone]
[link_ProductVersion.milestone.name]
[link_ProductVersion.milestone.nameProject]

The log file is like:
TinyButStrong Error in field [link_ProductVersion.idMilestone...]: item 'idMilestone' is not an existing key in the array.
TinyButStrong Error in field [link_ProductVersion.milestone.name...]: item 'milestone' is not an existing key in the array.

A change in tbs_class.php shows that only fields of a link are allowed for every kind of link.
LINE:  1203              
if (is_array($Value)) {
     $json = json_encode($Value); 
     $this->meth_Misc_Alert($Loc,'-ARR:'.$json,true);
LOG OUTPUT:
{
  "id": 14389,
  "ref1Type": "Product",
  "ref1Id": "681",
  "ref2Type": "ProductVersion",
  "ref2Id": "2685",
  "comment": null,
  "creationDate": "2022-08-04 14:31:29",
  "idUser": "1",
  "nameUser": "_",
  "ref1Name": "ST-User Interface Design",
  "ref2Name": "ST-Ekran çıkartılması",
  "refType": "ProductVersion",
  "refId": "2685",
  "refName": "ST-Ekran çıkartılması",
  "refTypeName": "Product Version",
  "refStatus": "New",
  "refResponsible": "Yasin YILMAZ",
  "refInitialDueDate": null,
  "refActualDueDate": "",
  "refDate": "",
  "refDescription": "Description asda fasf asdfasdfsad"
}

And tbs does not allow us to jump from Product.productVersion.milestone.name style directly.
If a tinybutstrong expert can help us, how to jump from Product to ProductVersion and go further deep recursively. 
It seems that with tbs we can call php functions to go next objects in hyearchy, But it is too complex for me.

If anyone has an example, it will help the community a lot.

I am trying to get full Product Documentation directly from Projeqtor, such as the whole project documentation, including requirements, milestones and component in a single file.
i believe it is a very cool feature...
Yasin
 

It is not a TBS issue.
It is a template report limit.
Read manual : Template report can extract data of one item (detail of element) or list of items.
If cannot get whole structure of a given objets with sub-objects.