Sorry for the poor English (i'm using translator) and also for the code; I still have some difficulties with JS and I’ve been using ChatGPT to help.
But I needed a new solution to print child rows in DataTables 2.x.
I arrived at this result, which seems to work, and I wanted to share it here as a tip in few steps:

1. Create a format function
   The parameter d represents the row’s data:

function format(d) {
    return 'Extra: ' + Math.random().toFixed(6);
}

1. Add a print button in the layout
   Use the format function to generate content for each row:

buttons: [
    {
        key: 'print',
        extend: 'print',
        className: 'btn btn-sm btn-secondary',
        exportOptions: { columns: ':visible' },
        customize: function (win, conf, api) {

            api.rows().every(function () {
                var extra = format(this.data());
                if (!extra) return;

                $(this.node()).after(
                    '<tr>' +
                        '<td colspan="100%" style="padding:3px 6px; border-bottom:2px solid #ddd;">' +
                            extra +
                        '</td>' +
                    '</tr>'
                );
            });

        }
    }
]

1. Initialize click events for showing/hiding child rows

table.on('click', 'tbody td.dt-control', function () {
    var row = table.row($(this).closest('tr'));
    var extra = getDetails(row.data());

    if (row.child.isShown()) {
        row.child.hide();
    } else {
        row.child(extra).show();
    }
});