LN-CB3S Module Pinout and Flashing Issues on Tuya Wall Switch – Any Documentation?

Any info on this module?

I could not find any information by googling "LN-CB3S."

It seems that this module has different pin labeling (and/or different pinouts) from CB3S module.

I connected A2 and A3 pins to TX and RX (and also tried to RX and TX) of my USB-to-serial (and also CEN to GND), but I cannot get it to enter flash mode.

This module is from a Tuya wall switch. Since I could not flash this module with any open-source firmware, I had to replace it with ESP-12F.

Any info would be appreciated.

Judging from module and pin names - LN882H.
Default RX/TX are for flashing (and app uart, if used), log should be at B9.

Backup can be taken with BK7231GUIFlashTool, chip enters flashing mode with A9 pulled down on boot

Interesting, looks like LN882H CB3S version. Can you try to take a backup with our flasher?
https://github.com/openshwprojects/BK7231GUIFlashTool