Assuming you have downloaded the correct UPDATE.BIN for your B311221 variant.

Post-Unlock Checklist:

Certain forums (like 4pda or XDA-developers) have developers who create "hybrid" firmware. For example: B311221-607_UPDATE_21.328.01.00.1946_MZ14. This firmware combines the latest modem firmware from the European B311 with the UI from the global model.

Risks: Requires a bootloader unlock code (V300R001). Reward: Exclusive features like VoLTE toggle and 5G neighbor cell monitoring.

This is the proprietary method used by advanced users. Note: I cannot distribute copyrighted firmware files here, but I will show you the exact process and where to find the correct tools.