The company had previously tried to block access to the bootloader on its smartphones, but only now with the next update the only loophole in the system was securely covered.
Unlocking the bootloader allows you to install third-party software on your device, greatly expanding its original functionality. With the so-called "custom recovery" you can get ROOT-rights, install third-party firmware, change system settings, and generally install any software.
The owners of Nokia smartphones have already written a petition to cancel the bootloader lock. But for now, you can only reflash the smartphone in Nokia's authorized service centers.