add_filter( 'frm_is_field_hidden', 'mark_recaptcha_hidden', 20, 2 );
function mark_recaptcha_hidden( $hidden, $field ) {
  $is_api_request = defined( 'REST_REQUEST' ) && REST_REQUEST;
  if ( FrmField::is_field_type( $field, 'captcha' ) && $is_api_request ) {
    $hidden = true;
  }
  return $hidden;
}