SELECT 
  cscart_bm_layouts.* 
FROM 
  cscart_bm_layouts 
WHERE 
  1 
  AND cscart_bm_layouts.company_id = 1 
  AND is_default = 1 
  AND theme_name = 'ap_theme'

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_bm_layouts",
      "access_type": "ref",
      "possible_keys": [
        "is_default"
      ],
      "key": "is_default",
      "used_key_parts": [
        "is_default",
        "company_id"
      ],
      "key_length": "5",
      "ref": [
        "const",
        "const"
      ],
      "rows": 3,
      "filtered": 100,
      "attached_condition": "(`_testcscart`.`cscart_bm_layouts`.`theme_name` = 'ap_theme')"
    }
  }
}