have you tried to disconnect everything from M5StickCPlus2 and fully powering it off by pressing and holding the power button?

Also have you tried to erase flash using M5Burner before installing UIFlow2 firmware?

BTW: I did a test and installed ESPHome basic firmware, then installed UIFlow2.3.8 firmware and then ran M5StickCPlus2_GPIO32_GPIO33_ON_OFF_UiFlow2.2.0 from Project Zone without issue, e.g GPIO32 and GPIO33 toggle just fine between 0 V and 3.3 V.

Note: While ESPHome was installed GPIO32 measured something like 0.2 V.

Thanks
Felix

your I2C scan code works for me (internal and Grove).
Internal I get:

Scanning for I2C devices ...
I2C device found at address 0x51
I2C device found at address 0x68

Grove (with ENV IV attached) I get:

Scanning for I2C devices ...
I2C device found at address 0x44
I2C device found at address 0x76

and your Groove GPIO test works for me as well, both GPIO32 and GPIO33 toggle between 0 and 3.3 V.

Just to clarify; does the internal I2C scan work with your M5StickCPlus2?

If yes, then the failing Grove I2C scan and the GPIO test showing a too low voltage on GPIO32 would indicate that GPIO32 got damaged somehow.

But then again, you tested with two M5StickCPlus2 and they both exhibit this behavior, so I am not sure.

Thanks
Felix

I started with this code to do an I2C wire scan. It returns Error 5 at all addresses, No I2C devices found when I have I2C devices connected.

#include <Arduino.h>
#include <Wire.h>

  // Board Pin Definitions
#define PIN_POWER_HOLD 4
#define PIN_LCD_BL 27
  //Internal I2C BUS 6-Axis posture sensor (MPU6886) & RTC (BM8563)
#define PIN_INTERNAL_SDA 21
#define PIN_INTERNAL_SCL 22
  //Grove Connector I2C BUS (Port A)
#define PIN_GROVE_SDA 32
#define PIN_GROVE_SCL 33

void wireScanTest() {
  Wire.begin(PIN_GROVE_SDA, PIN_GROVE_SCL, 400000);
  //Wire.begin(PIN_INTERNAL_SDA, PIN_INTERNAL_SCL, 400000);

  byte error, address;
  int nDevices = 0;

  delay(5000);

  Serial.println("Scanning for I2C devices ...");
  for (address = 0x01; address < 0x7f; address++) {
    Wire.beginTransmission(address);
    error = Wire.endTransmission();
    if (error == 0) {
      Serial.printf("I2C device found at address 0x%02X\n", address);
      nDevices++;
    } else if (error != 2) {
      Serial.printf("Error %d at address 0x%02X\n", error, address);
    }
  }
  if (nDevices == 0) {
    Serial.println("No I2C devices found");
  }
}

void setup() {
  pinMode(PIN_POWER_HOLD, OUTPUT);
  digitalWrite(PIN_POWER_HOLD, HIGH);
  pinMode(PIN_LCD_BL, OUTPUT);
  digitalWrite(PIN_LCD_BL, HIGH);
  Serial.begin(115200);

  wireScanTest();
}

void loop() {}

So I made this to test the pins and i get the strange voltage on pin 32.

#include <Arduino.h>
#include <Wire.h>

  // Board Pin Definitions
#define PIN_POWER_HOLD 4
#define PIN_LCD_BL 27
  //Grove Connector I2C BUS (Port A)
#define PIN_GROVE_SDA 32
#define PIN_GROVE_SCL 33

void setup() {
  pinMode(PIN_POWER_HOLD, OUTPUT);
  digitalWrite(PIN_POWER_HOLD, HIGH);
  pinMode(PIN_LCD_BL, OUTPUT);
  digitalWrite(PIN_LCD_BL, HIGH);
  pinMode(PIN_GROVE_SDA, OUTPUT);
  digitalWrite(PIN_GROVE_SDA, HIGH);
  pinMode(PIN_GROVE_SCL, OUTPUT);
  digitalWrite(PIN_GROVE_SCL, HIGH);

  Serial.begin(115200);
}

void loop() {
  delay(5000);
  digitalWrite(PIN_GROVE_SDA, LOW);
  digitalWrite(PIN_GROVE_SCL, LOW);
  delay(5000);
  digitalWrite(PIN_GROVE_SDA, HIGH);
  digitalWrite(PIN_GROVE_SCL, HIGH);
}

both GPIO32 and GPIO33 work for me in UIFlow2. Please find an example in the Project Zone called: M5StickCPlus2_GPIO32_GPIO33_ON_OFF_UiFlow2.2.0
If you are using Arduino instead then could you share your code?

Thanks
Felix