In short: Downgrading would require physically replacing the APU, Syscon chip, and NOR—essentially building a new console.
If you want, I can instead:
If you updated to an intermediate version (e.g., 9.03) before reaching 10.50, the 9.00 backup has already been overwritten and cannot be recovered. Technical Requirements ps4 downgrade 10.50 to 9.00
If you are on firmware 10.50 and looking to downgrade to 9.00: In short: Downgrading would require physically replacing the