Row widget contents are not getting displayed

The problem is that the row isn't used anywhere. So instead of using this so called _buildPosts you can simply return a listView.builder. Checkout the code below:

I have added 2 sets of solutions below:

 ListView.builder(
    itemCount: posts.length,
    itemBuilder: (context, index) {
     
        return Card(
          shadowColor: Colors.white,
          color: const Color(0xFF303030),
          elevation: 1,
          child: IntrinsicHeight(
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                Column(
                  children: [
                     Container(
              child: const Text(
                'Did',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
                    Text(
                      posts[index].Did,
                      style: const TextStyle(
                        fontWeight: FontWeight.bold,
                        color: Colors.white,
                      ),
                    ),
                  ],
                ),
                Column(
                  children: [
                     Container(
              child: const Text(
                'Dname',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
                    Text(
                      posts[index].Dname,
                      style: const TextStyle(
                        fontWeight: FontWeight.bold,
                        color: Colors.white,
                      ),
                    ),
                  ],
                ),
                Column(
                  children: [
                    Container(
              child: const Text(
                'Age',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
                    Text(
                      posts[index].Age,
                      style: const TextStyle(
                        fontWeight: FontWeight.bold,
                        color: Colors.white,
                      ),
                    ),
                  ],
                ),
              ],
            ),
          ),
        );
      
    },
  ),

This is the most simplest approach but as per your answer there is another complex approach:

ListView.builder(
    itemCount: posts.length * 2,
    itemBuilder: (context, index) {
      if (index.isOdd) {
        return Card(
          shadowColor: Colors.white,
          color: const Color(0xFF303030),
          elevation: 1,
          child: IntrinsicHeight(
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                Text(
                  posts[index*2].Did,
                  style: const TextStyle(
                    fontWeight: FontWeight.bold,
                    color: Colors.white,
                  ),
                ),
                Text(
                  posts[index*2].Dname,
                  style: const TextStyle(
                    fontWeight: FontWeight.bold,
                    color: Colors.white,
                  ),
                ),
                Text(
                  posts[index*2].Age,
                  style: const TextStyle(
                    fontWeight: FontWeight.bold,
                    color: Colors.white,
                  ),
                ),
              ],
            ),
          ),
        );
      } else {
        return Row(
          //This row is not getting displayed
          children: [
            Container(
              child: const Text(
                'Did',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
            Container(
              child: const Text(
                'Dname',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
            Container(
              child: const Text(
                'Age',
                style: TextStyle(
                  color: Colors.white,
                ),
              ),
            ),
          ],
        );
      }
    },
  ),

It can't be displayed because it isn't used anywhere! Your _buildPosts() only returns Listview.builder(). Wrap your List view.builder() inside a Column, then move your Row() inside that Column() above Listview.builder().

The best and optimal solution for your case is use DataTable .It makes table data visualization so simple and it is very easy to use

@override
Widget build(BuildContext context) {
return DataTable(
  columns: const <DataColumn>[
    DataColumn(
      label: Text(
        'Did',
        style: TextStyle(fontStyle: FontStyle.italic),
      ),
    ),
    DataColumn(
      label: Text(
        'Dname',
        style: TextStyle(fontStyle: FontStyle.italic),
      ),
    ),
    DataColumn(
      label: Text(
        'Age',
        style: TextStyle(fontStyle: FontStyle.italic),
      ),
    ),
  ],
  rows: const <DataRow>[
    DataRow(
      cells: <DataCell>[
        DataCell(Text('1')),
        DataCell(Text('Raj')),
        DataCell(Text('34')),
      ],
    ),
    DataRow(
      cells: <DataCell>[
        DataCell(Text('Janine')),
        DataCell(Text('43')),
        DataCell(Text('Professor')),
      ],
    ),
    DataRow(
      cells: <DataCell>[
        DataCell(Text('William')),
        DataCell(Text('27')),
        DataCell(Text('Associate Professor')),
      ],
    ),
  ],
);
} 

you can render a list into row like this

rows: _list.map((cita) => DataRow(
                        cells: [
                          DataCell(Text(_list.telefono ?? '',style: const 
                          TextStyle(
                              fontSize: 18,color: Colors.black
                          ))),
                          DataCell(Text(_list.nombre ?? '',style: const 
                          TextStyle(
                              fontSize: 18,color: Colors.black
                          ))),
                         DataCell(Text(_list.nombre ?? '',style: const 
                          TextStyle(
                              fontSize: 18,color: Colors.black
                          ))),
                       ]
                    )

I know my answer is far away from your asking question but this is the best approach to handle data table in flutter