SELECT 
  cscart_attachments.*, 
  cscart_attachment_descriptions.description 
FROM 
  cscart_attachments 
  LEFT JOIN cscart_attachment_descriptions ON cscart_attachments.attachment_id = cscart_attachment_descriptions.attachment_id 
  AND lang_code = 'en' 
WHERE 
  object_type = 'product' 
  AND object_id = 64908 
  AND type = 'M' 
  AND (
    usergroup_ids = '' 
    OR FIND_IN_SET(0, usergroup_ids) 
    OR FIND_IN_SET(1, usergroup_ids)
  ) 
  AND status = 'A' 
ORDER BY 
  position

Query time 0.00058

JSON explain

{
  "query_block": {
    "select_id": 1,
    "read_sorted_file": {
      "filesort": {
        "sort_key": "cscart_attachments.position",
        "table": {
          "table_name": "cscart_attachments",
          "access_type": "ref",
          "possible_keys": ["object_type", "type"],
          "key": "object_type",
          "key_length": "95",
          "used_key_parts": ["object_type", "object_id"],
          "ref": ["const", "const"],
          "rows": 4,
          "filtered": 99.86836243,
          "index_condition": "cscart_attachments.object_type = 'product'",
          "attached_condition": "cscart_attachments.object_type <=> 'product' and cscart_attachments.object_id <=> 64908 and cscart_attachments.`type` = 'M' and (cscart_attachments.usergroup_ids = '' or find_in_set(0,cscart_attachments.usergroup_ids) or find_in_set(1,cscart_attachments.usergroup_ids)) and cscart_attachments.`status` = 'A'"
        }
      }
    },
    "table": {
      "table_name": "cscart_attachment_descriptions",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["attachment_id", "lang_code"],
      "ref": ["cscart_migrate.cscart_attachments.attachment_id", "const"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "trigcond(cscart_attachment_descriptions.lang_code = 'en')"
    }
  }
}

Result