Warning: flashing firmware can permanently brick your device if done incorrectly. Back up any important data and proceed only if you accept the risk.
After testing over a dozen sources (including the notorious Chinese forums Baidu Pan and 4PDA), these are the for the MXQ Pro 4K RK3228A as of this year. mxq+pro+4k+rk3228a+firmware+download+best
When searching for the file to ensure you have the correct version for your specific board, check for these details in the file name or description: Warning: flashing firmware can permanently brick your device
To install these firmwares, you will typically need a Windows PC and the following Rockchip-specific utilities: mxq+pro+4k+rk3228a+firmware+download+best