Comm.begin(115200, SERIAL_8N1,TX_pin,RX_pin); // TX RX

Comm.print("AT+IPR=115200\r"); // Set text mode

Last command should return an OK. If not, it could be that you have mixed up TX and RX pins or a power issue.

To read the reply from the module you could use something like this :
while (millis()<wait_until)
{
while (Comm.available())
{
ccc=Comm.read();
//Serial.print(ccc);
if (k<buffer_size-1)
{
Receive_buffer[k]=ccc;
k++;
}
}
Receive_buffer[k]=NULL;
if (strstr(Receive_buffer,StopCharArray)!=NULL)
{
//Serial.println("OK found");
// SIM7600_Error=0;
Receive_buffer[k]=NULL;
return false;
}
}

which M5 core device are you using? M5Stack (Base, Fire, ...) or M5Core2 or M5CoreS3?

Also make sure your SIM card has the PIN disabled.

Thanks
Felix