I mostly understand how these fuses prevent say downgrading firmware, but could t a Chinese firm looking to clone one of these also just clone the number of blow. Fuses equally trivially if the goal is just an also working device with stock firmware?

The security researcher, LimitedResults, coordinated disclosure with Espressif on their advisory and details of the exploit. The attack works against eFuse, a one-time programmable memory where data can be burned to the device.

By burning a payload into the device’s eFuse, no software update can ever reset the fuse and the chip must be physically replaced or the device discarded. A key risk is that the attack does not fully replace the firmware, so the device may appear to work as normal.

Why does a random esp32 chip need efuses in the first place??