While a software-based secure boot exploit has been in development, it is not currently in a functional state for public release. Usability Limitations on Stock Firmware

The Priv was designed with "DTEK" security, which verifies every layer of the boot process from the hardware up. Unlike most Android phones, there is no official bootloader unlock code provided by BlackBerry, and no software exploit currently exists to bypass this "root of trust".

Use the built-in DTEK by BlackBerry app to manage permissions, as modern apps often over-request data on older OS versions. Why It's Difficult