The only known way to downgrade involves highly technical hardware modification:
Do not update past 9.60. If a new exploit is found, it will target lower firmwares first. how to downgrade ps4 9.60 to 9.00
You cannot simply "install" an older firmware version from a USB drive on a PS4. Sony's security prevents any software-only downgrade to protect against jailbreaking. The only known way to downgrade involves highly
Downgrading a PS4 from firmware version 9.60 to 9.00 can be a challenging and complex process, but it's possible with the right tools and guidance. Before we dive into the steps, it's essential to understand the risks involved and the requirements for a successful downgrade. how to downgrade ps4 9.60 to 9.00