Huawei STK-L21 (Y9 Prime 2019) FRP Solution.
 

Checking fastboot device.....OK
Reading info.....OK
Device Model: STK-L21
Device Firmware: :STK-L21M 9.1.0.312(C185E2R2P1)
Device FB Lock: LOCKED
Device USER Lock: LOCKED
Device Lock: locked
Operation {Read info} ID: DE955B34A216A77B
Elapsed time 00:00 -- Version 1.8.2
=========================
downgrade with this
https://easy-firmware.com/index.php?...file&id=173652
Stark-L21MEA 9.1.0.223(C185E2R4P1)
Use safe mode method to bypass FRP
ASK TO EFT FOR FILE NOT ME
=========================
Checking fastboot device.....OK
Reading info.....OK
Device Model: STK-L21
Device Firmware: :STK-L21M 9.1.0.223(C185E2R4P1)
Device FB Lock: LOCKED
Device USER Lock: LOCKED
Device Lock: locked
Operation {Read info} ID: DE955B34A216A77B
Elapsed time 00:00 -- Version 1.8.2

Checking fastboot device.....OK
Reading info.....OK
Device Model: STK-L21
Device Firmware: :STK-L21M 9.1.0.351(C185E2R4P1)
Device FB Lock: LOCKED
Device USER Lock: LOCKED
Device Lock: locked
Operation {Read info} ID: 167F6ED785370281
Elapsed time 00:00 -- Version 3.1.2
===========================
Checking fastboot device.....OK
Reading info.....OK
Device Model: STK-L21
Device Firmware: :STK-L21M 9.1.0.223(C185E2R4P1)
Device FB Lock: LOCKED
Device USER Lock: LOCKED
Device Lock: locked
Operation {Read info} ID: 03191EBBB6F977C7
Elapsed time 00:00 -- Version 3.1.2Checking fastboot device.....OK
============================
AFTER DOWNGRADE USE SAFE MODE FOR REMOVE FRP