Changing the software version to a previous one will be impossible — unless you replace the motherboard.
OnePlus smartphone owners using ColorOS have noticed that version 16.0.3.500/501/503 implements an Anti-Rollback (ARB) mechanism. This blocks the ability to downgrade to previous software versions.
The restriction is hardware-based: after installing the specified versions, a physical fuse is triggered in the Qualcomm processor’s Fuse Programmable Read-Only Memory. Currently, the only known way to reverse this is by replacing the motherboard.
If you attempt to lower the firmware version after installing software with active ARB, the smartphone will be bricked beyond recovery. Installing older custom ROMs is also impossible. Authors on the XDA forum point out that third-party bypass tools like Chimera Firehose do not help.
Currently, the update is rolling out for the OnePlus 13/13T, OnePlus 15, and the Ace 5 series. While global versions on OxygenOS are currently safe, this could change at any time.
