[BK7231N] Major Tech MTS21 - custom firmware with RN8209C UART1 driver?

"I have a Major Tech MTS21 energy meter containing a CBU module directly wired to an RN8209C metering chip via UART1 (P10/P11). Can someone please provide a custom compilation of the latest BK7231N firmware containing #define ENABLE_DRIVER_RN8209 1 enabled?"
AI: Which firmware project/repository and target are you referring to, e.g. OpenBeken for BK7231N/CBU, and do you need a

.bin

for UART flashing or OTA?
Built on Aug 2, 2026, 19:38:07, version 1.18.300. OTA, please.
AI: Have you already dumped the original firmware/config/calibration data from the MTS21, and can you share the current pin/config template you are using for P10/P11 UART1 and RN8209C?
Current dump from original firmware:
Sorry, no meaningful pin data found. This device may be TuyaMCU or a custom one with no Tuya config data.
No module information found.
And the Tuya section starts, as usual, at 2023424.

I didn't actually realise this was a driver OBK had. I will enable and give build file.

ChatGPT gave a 3/10 rating on review. I wonder if it'll work OK

Added after 1 [hours]:

attached.