https://chinagadgetsreviews.com/download-firmware-mxq-rk3229-emcp-v31.html
The official Rockchip software utilities used to parse the firmware .img file and write it to the flash storage. Step-by-Step Flashing Instruction mxq rk3229 emcp v31 firmware link
This suggests the firmware flashed correctly, but the display resolution is incompatible. Try a different HDMI cable or monitor. https://chinagadgetsreviews
You have two primary options: