Should you refrain from overtaking in this situation?

Yes, in this situation you must absolutely refrain from overtaking. The image in the left mirror clearly shows that the vehicle in the left lane has already begun the overtaking manoeuvre. According to Art. 24 para. 1 pt. 2 of the Road Traffic Act, a driver is forbidden to overtake if the driver behind them has already started this manoeuvre. Changing lanes at this moment would force the other vehicle to brake sharply and would risk a collision.