You can select the field events.message to export all event messages in the timeline which will include the comments.

To only export the Timeline comments specifically, you can use the formula below in the Calculated Fields:

", ".join([i.message for i in load_json_data({{ events }}) if i.action == "comment"])

There's also a template you can use called "Orders with Timeline Comments (Last 30 Days)" which will only include orders that contain a comment and can be customized further.

Please note, however, that we can only export the comment date and text.  We can't export the name of the user/Staff Member who left the comment or files attached to the comment.