Table Configuration Array (TCA)

Set the renderType of a single-select to icon in order to make icons selectable by backend users. All configuration options for a standard single-select field can be applied.

EXT:my_ext/Configuration/TCA/tx_myext_elements_icon.php

[
    'columns' => [
        'icon_select' => [
            'label' => 'Icon selector',
            'config' => [
                'type' => 'select',
                'renderType' => 'icon',
                'items' => [
                    ['label' => 'Choose icon…', 'value' => '']
                ],
                'itemGroups' => [
                    'icomoon' => 'Icomoon'
                ]
            ]
        ]
    ]
]