Ok, thanks for the clarification. I was under the impression that things like flash encryption keys were stored in block1, based on the following info I found online :

The eFuses controller is in charge to manage the eFuses arrays and has 4 eFuses blocks, each one is 256 bits length (not all bits ...

Apparently I am misunderstanding the use of ESP32 eFuses.
I want to store some unique identifier in block3 of the ESP32 eFuses, and protect this data from being copied to another ESP32 board (which would make it non-unique). But apparently making the block read-protected also stops me from reading ...