Let me save you hours of frustration:
You want to go back. You want to downgrade.
Firmware 10.50, however, patched the critical BD-JB (Blu-ray Disc Java) exploit used in 9.00. Sony also introduced stricter anti-rollback mechanisms. Once you install 10.50, the console physically burns "fuses" (e-fuses) inside the Syscon chip that prevent the system from ever booting an older firmware again. If you search YouTube, you will see videos titled "PS4 Downgrade 10.50 to 9.00 in 2 Minutes!" with a flashing download link. These are 100% scams or virus traps. ps4 downgrade 10.50 to 9.00
You must modify the Syscon dump to reset the "minimum version" counter from 0xA (10.50) back to 0x9 (9.00). This requires hexadecimal editing.
However, if you are a hardware modder or a tinkerer, there is a narrow, dangerous path. Here is the full breakdown of why 10.50 is a prison, and the one extreme method to escape it. Firmware 9.00 is the holy grail for the PS4 homebrew community. It supports a stable jailbreak, allowing you to run backup loaders, emulators, and custom mod menus. Let me save you hours of frustration: You want to go back
You need to connect 4-5 tiny wires (3.3V, GND, SWDIO, SWCLK, and RESET) from your Teensy to the Syscon. One wrong solder bridge will kill your console.
Using your programmer, read the current e-fuse configuration. This tells you how many times the console has been updated. Sony also introduced stricter anti-rollback mechanisms
Write the modified firmware back to the Syscon chip. If you lose power during this step, the console becomes a paperweight.