Because Nokia locks bootloaders on most of its devices (including the G21), official flashing typically requires authorized tools or service-center access. Unofficial methods exist but come with limitations.
ResearchDownload is the official flash tool from Unisoc, used by engineers and service centers. It communicates directly with the phone’s preloader or download mode. nokia g21 flash tool
For the Nokia G21, users typically seek a flash tool for one of the following reasons: Because Nokia locks bootloaders on most of its
Launch the ResearchDownload.exe or SPD Flash Tool as an administrator. nokia g21 flash tool