Never relock the bootloader on a non-stock system. You will hard-brick the device.
On paper, it sounds like the perfect smartphone. You get the legendary KEY2 hardware—a 4.5-inch screen, a hub of programmable convenience keys, and that glorious, clicky keyboard—stripped of its aging, insecure Android 8.1 Oreo. In its place, you install LineageOS, the lightweight, privacy-respecting ROM that could breathe new life into the device, potentially upgrading it to Android 11, 12, or even 13. blackberry key2 lineageos install
A software-based unlock method allows users to bypass manufacturer signature checks to flash custom images. Availability: Never relock the bootloader on a non-stock system