for loop only return first element of List inside ListView.builder but it works for in build Widget

You probably want to use it like this:

ListView.builder(
    itemCount: eventList.length,
    itemBuilder: (context, index) {
      print('------${eventList[index].eventTitle}------');
      return Text(eventList[index].eventTitle);
    }
),

Add itemCount inside ListView.builder()

Widget build(BuildContext context) {
    List eventList = [
      TimelineModel(              
          eventTitle: 'first',),
      TimelineModel(              
          eventTitle: 'second'),
    ];    
    return GetBuilder<TimelineController>(builder: (controller) {
          for(var e in eventList){
            print('???${e.eventTitle}'); // here loops work
          }
          return Scaffold(          
            body: Container(              
              child: Stack(
                children: [                
                  ListView.builder( 
                    itemCount: eventList.length,            
                    itemBuilder: (context, index) {
                      for (var event in eventList) 
                          print('------${event.eventTitle}------'); // here loop will only return first element                       
                  ),                  
                ],
              ),
            ),
          );
        }
    );

Try the following code:

ListView.builder(
  itemCount: eventList.length,
  itemBuilder: (context, index) {
    final event = eventList[index];

    print('------${event.eventTitle}------');
    return Text(event.eventTitle);
  },
),