Need to be fully stock
Restoring device to factory condition , see this thread
Download PHH-AOSP 10
Download will be a compressed file *.gz , ectract the *.img file from inside
fastboot flash system **extracted-GSI.IMG** fastboot oem reboot recovery
my tests trying to complete these steps with twrp all end with unknown imei.
V203 boots with only found issue is the fingerprint sensor Not working. For me i feel mtk devices are not secure anyway, the fingerprint sensor is more of a gimmick, so if it is not working, i do not care.
Current version v215 tested by and boots fine.