Hello! You can use the gform_field_choice_markup_pre_render filter to modify the markup for your checkbox choices. If you call it without adding a form ID to the filter, it should work site wide. Something like this should work for your case:
add_filter( 'gform_field_choice_markup_pre_render', function ( $choice_markup, $choice, $field, $value ) {
if ( $field->get_input_type() === 'checkbox' ) {
$icon = '<span class="checkbox" role="none">
<svg class="brei-icon brei-icon-check" focusable="false">
<use xlink:href="#brei-icon-check"></use>
</svg>
</span>';
return str_replace( '</label>', "$icon</label>", $choice_markup );
}
return $choice_markup;
}, 10, 4 );