You could use the popup menu widget for it.
https://marketplace.mendix.com/link/component/115826
Add the widget in the page or navigation lay-out where you have your bell image now.
In the widget:
- Enable advanced options
- Add a menu item with on click action: 'Do nothing'
- Set the 'Open on' setting to 'Hover'
Place your bell image in section: 'The area to open or close the menu'.
Place your list with notifcations in section: 'Menu items/1/Content'.