Lock and unlock the bootloader | Android Open Source Project
Nokia (HMD Global) generally does not provide official bootloader unlock codes for its entry-level devices. For the Nokia 2.3 specifically: e/OS community No Official Support Nokia 2.3 Custom Rom
Given the difficulty of flashing custom software, users often turn to "software-only" optimizations to keep the device "snappy": Developer Options Lock and unlock the bootloader | Android Open