Before diving into the tools, it is crucial to understand what makes Nokia devices unique. Unlike many OEMs that use the standard MediaTek (SP Flash Tool) or Qualcomm protocols, HMD Global devices often employ a different partition layout and security architecture.
The Nokia G21 is powered by a Unisoc (formerly Spreadtrum) processor. This means standard tools like Odin (Samsung) or SP Flash Tool (MediaTek) will not work. You need software specifically designed to communicate with Unisoc chipsets and the Nokia bootloader. nokia g21 flash tool full
Disclaimer: Flashing your device will void your warranty (unless done by an authorized service center) and will erase all user data. Proceed at your own risk. Before diving into the tools, it is crucial
If you need a 100% official flash that restores the bootloader and locks it, Nokia uses OST LA (Online Service Tool LA). This is meant for service centers. It requires an authorized account. The Nokia G21 does not enter download mode
The Nokia G21 does not enter download mode via Volume buttons alone. You must use the specific "Emergency Download Mode" (EDL for Unisoc):