"Formatting the hard drive removes the firmware."
For 98% of users, the best "how to downgrade PS4 9.60 to 9.00" answer is: how to downgrade ps4 9.60 to 9.00
No publicly available software downgrader exists for any PS4 firmware above 7.55. Anyone selling a "9.60 to 9.00 downgrader tool" on eBay or YouTube is scamming you. "Formatting the hard drive removes the firmware