By not having Wifi conectivity, Is it possible to use an external RTC-Module(soldering to GPIO21 and GPIO22)?
Have someone written a code for this Situation??
Yes, it should be possible. But you need to take into account that those pins are also being used by the camera: https://randomnerdtutorials.com/esp32-cam-ai-thinker-pinout/
So, you need to write your code taken that into account.
If your RTC communicates using I2C communication protocol, you don’t necessarily need to use GPIO 22 and GPIO 21. You can use any other pins: https://randomnerdtutorials.com/esp32-i2c-communication-arduino-ide/