// Start I2C
  if (!M5.Ex_I2C.begin(I2C_NUM_0, 31, 32)) {
		Serial.println("Ex_I2C initialization failed!");
  } else {
    exI2CInitialized = true;
    Serial.println("Ex_I2C ok! ");
  }

In the modified I2C sensor code:

uint8_t TON_BME280::read8(byte reg) {
	return M5.Ex_I2C.readRegister8(BME280_ADDRESS, reg, 400000U);
}

This works on Arduino, RTC (internal) and BME280 (external) are available.

However, on PlatformIO same code, it does not work. The first call to battery status returns zeroes and subsequent I2C calls hang the system.

Why use PlatformIO then? It compiles quicker, more control over libraries possible (lvgl 8 or 9 etc)

Why use the same pins as internal for external I2C instead of two fresh ones?
Modules like relays or stepper controllers all use the 31 and 32 pins for I2C

platformio.ini:

[env:m5stack-tab5-p4]
platform = https://github.com/pioarduino/platform-espressif32/releases/download/stable/platform-espressif32.zip
board = m5stack-tab5-p4
framework = arduino

upload_port = COM12
monitor_port = COM12
upload_speed = 1500000
monitor_speed = 115200
build_type = debug
board_build.partitions = partitions.csv

lib_deps =
  lvgl/lvgl@^8.3.11
  paulstoffregen/OneWire@^2.3.8
  milesburton/DallasTemperature@^4.0.5