DISCLAIMER: You may brick/damage your box, do only if you know what you're doing and at your own risk
Only tested for H96 Max v58 (Rockchip RK3588).
You can find the latest stock at Firmware Download. It's the one for H96 Max V58 (RK3588).
See Booting for instructions.
Using RKDevTool on Windows you need to click firmware choose the file and press upgrade.