Flutter IconButton onPressed never fires

As I was unaware that ListTiles exists I implemented the following from scratch:

My widget-structure looks like this:

• StudiesItemWidget (equals scaffold of widget, contains the following three)
• StudiesItemDuration (equals leading number)
• StudiesItemDescription (equals main body of widget, containing description + date)
• StudiesItemRemove (equals trailing icon, on pressed should remove containing item from list)

Here’s the relevant code:

Provider for items containing the data for the widgets:

class StudyProvider with ChangeNotifier {
  List<StudiesItem> _studiesItemList = [
    /*StudiesItem(duration: 100, subject: 'AM', date: DateTime.now()),
    StudiesItem(duration: 100, subject: 'AM', date: DateTime.now()),
    StudiesItem(duration: 100, subject: 'POS', date: DateTime.now()),
    StudiesItem(duration: 100, subject: 'DBI', date: DateTime.now()),*/
  ];

  void addItem(StudiesItem studiesItem) {
    _studiesItemList.add(studiesItem);
    notifyListeners();
  }

  List<StudiesItem> get studiesItems {
    return List.unmodifiable(_studiesItemList);
  }
}

Main studies-item-widget:

class StudiesItemWidget extends StatelessWidget {
  final StudiesItem studiesItem;

  const StudiesItemWidget({
    Key? key,
    required this.studiesItem
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 5,
      child: Container(
        width: MediaQuery.of(context).size.width * 0.95,
        height: MediaQuery.of(context).size.height * 0.075,
        decoration: BoxDecoration(
            border: Border.all(color: Colors.grey),
            borderRadius: BorderRadius.all(Radius.circular(4))),
        child: Chip(
          label: Row(
            children: [
              StudiesItemDuration(timeAmount: studiesItem.duration),
              StudiesItemDescription(subject: studiesItem.subject, date: studiesItem.date),
              StudiesItemRemove(containingWidget: this)
            ],
          ),
          backgroundColor: Colors.white,
          shape: BeveledRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(4)),
          ),
        ),
      ),
    );
  }
}

Widget responsible for deletion:

class StudiesItemRemove extends StatelessWidget {
  final StudiesItemWidget containingWidget;

  const StudiesItemRemove({
    required this.containingWidget,
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    var studiesItems = Provider.of<StudyProvider>(context).studiesItems;

    return Expanded(
      child: Container(
        alignment: Alignment.centerRight,
        child: IconButton(
            onPressed: () {
              studiesItems.remove(containingWidget.studiesItem);                // ToDo: fix
            },
            icon: Icon(Icons.delete)
        ),
      ),
    );
  }
}

In case this is relevant, the list of widgets in the homepage gets built using the following snippet:

var studyProvider = Provider.of<StudyProvider>(context, listen: true);    
...
body: Column(
  children: [
    (studyProvider.studiesItems.isEmpty) ? EmptyStudiesText() : BarChartWidget(),
    Expanded(
      child: ListView.builder(
        scrollDirection: Axis.vertical,
        itemCount: studyProvider.studiesItems.length,
        itemBuilder: (context, index) {
          return StudiesItemWidget(studiesItem: studyProvider.studiesItems[index]);
        },
      ),
    ),
  ],
),

Clicking the icon doesn’t do anything. As not even printing "remove pressed" on pressed I believe the method doesn’t get called at all. Passing the function in different ways (not sure I said that correctly but I mean: "() { code(); } or () => code()") also doesn’t make a difference.

Can someone help me out? Thanks

Note:
I just changed the remove-call to directly call the providers removeItem function (still doesn’t work):

onPressed: () {
    studiesItemProvider.removeItem(containingWidget.studiesItem); // ToDo: fix
},
...
bool removeItem(StudiesItem studiesItem) {
    var success = _studiesItemList.remove(studiesItem);
    notifyListeners();
    return success;
} 

Second Note:
As per request, here is my StudiesItem class:

class StudiesItem {
  int duration;
  final String subject;
  final DateTime date;

  StudiesItem({
    required this.duration,
    required this.subject,
    required this.date,
  });

  StudiesItem.clone(StudiesItem original):
      this(
        subject: original.subject,
        duration: original.duration,
        date: original.date
      );

  @override
  String toString() {
    return 'StudiesItem{duration: $duration, subject: $subject, date: $date}';
  }

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is StudiesItem &&
          runtimeType == other.runtimeType &&
          duration == other.duration;

  @override
  int get hashCode => duration.hashCode;

  static StudiesItem mergeItems(StudiesItem item1, StudiesItem item2) {
    assert(item1 != item2);

    return StudiesItem(
        duration: item1.duration + item2.duration,
        subject: item1.subject,
        date: item1.date
    );
  }
}

The mergeItems function is used in another (fully working) code-segment to summarize the total data. It should not interfere with the rest of the app.