For 99% of users, the safest and recommended way to update firmware is via the Over-The-Air (OTA) mechanism built into Android.
The Nokia G21 originally launched with Android 11. Since then, it has received significant updates: Android 13: nokia g21 firmware
Some users reported being "stuck" on old patches for months before receiving a sudden wave of updates. Clean, near-stock Android with zero ads in the interface. For 99% of users, the safest and recommended
Fastboot variables on Nokia G21 (locked state) For 99% of users