SELECT 
  cscart_bm_layouts.* 
FROM 
  cscart_bm_layouts 
WHERE 
  1 
  AND is_default = 1 
  AND theme_name = 'vietpom_theme' 
  AND storefront_id = 1

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_bm_layouts",
      "access_type": "ALL",
      "possible_keys": ["is_default"],
      "rows": 8,
      "filtered": 50,
      "attached_condition": "cscart_bm_layouts.is_default = 1 and cscart_bm_layouts.storefront_id = 1 and cscart_bm_layouts.theme_name = 'vietpom_theme'"
    }
  }
}