Data seen in mariaDB but can not access in endPoint API

Use this response type and return it

from werkzeug.wrappers import Response
from frappe.utils import response as r

Don’t return simply a dict

If the above documentation is not working try this:

import frappe
from frappe.utils import response

@frappe.whitelist(allow_guest=True)
def get_item_details(item=None):
  Item = frappe.db.sql("select * from tabItem", as_dict=True )
  response['http_status_code'] = 200
  response['data'] = Item
  return

Note: If its not working add method type and hit with respective method like this

@frappe.whitelist(allow_guest=True, method='POST')