Download Android Pie 9.0 stock firmware for X99 MAX Plus TV Box from here or here. Download previous firmware from here. Download Amlogic USB Burning Tool v2.1.6 from here or download Amlogic Burn_Card_Maker v2.0.2 from here.
Archive name: x99-s905x3_d4_sp6330_100m_20200917_r1(x99max+)
Archive file size: 670 MB
Model: X99 MAX Plus 4GB + 32GB / 4GB + 64GB / 4GB + 128GB TV Box
Platform: AMLogic S905x3
System: Android version 9.0
Build number: franklin-userdebug 9 PPR1.180610.011 20200917 test-keys
Caution Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data. BTW, a link doesn’t last for ever.