Mi8 Pro ( equuleus )softbrick cannot upgrade android Pie and Q

[codonline0807]

hi all
my phone Xiaomi Mi8 pro Equuleus was flashed custom Oxygen os and bricked my phone.
Now i cannot install android 9 and 10 miui stock firmware.
Everytime i install Mi8pro fastboot firmware android 9 , android 10,
get stuck into Bootloader.I tried <Wipe /format > in recovery ,but did not boot to system.
always loop into fastboot mode.
Only android 8.1 rom boot to system successfully.
I cannot upgrade to pie and Q rom.
help me .