[BK7231N] How to flash Taxnele TVPS1-63LW - UART no response, 3.3V at 1.xV

Hello,
I'm interested in flashing Taxnele TVPS1-63LW Wi-Fi Multi-Function Protector. So far I was able to disassemble it and solder pins to the only possible (to me) interface. Then I tried to read logs or to backup the original firmware with BK7231Flasher, but no luck.
I tried TX/RX swapping, tracing pins from UART to the CBU was a bit strange - on the 3.3 V of the CBU I can measure only 1.x V (can't remember the exact measure).
I also tried to undock the display board from the one with the CBU on it, but there is no change.
I read that the MCU could take over the tx/rx communication, so that's why I can't communicate with the CBU.

Does anyone has some ideas?

UART is connected to MCU, so RX1/TX1 lines are in use:

You need to cut this connection first. You can either desolder CBU, or the MCU, or maybe those two resistors which luckily are there in place:

Remember to take 2 MB backup of flash before you burn new firmware.