is it possible to create a duplicate page for the existing http://localhost:8000/desk#query-report/Balance Sheet? .How is it possible?Please help me
Yes, you can do it inside your custom apps.
For reference you can check rigpl-erpnext/rigpl_erpnext/rigpl_erpnext/report at master · erpnext-apps/rigpl-erpnext · GitHub
It is a custom app made by Rohit Industries.