Is it permissible for a traveler covering a distance of 800 km to pray Dhuhr shortened instead of Jumu'ah if the day of travel falls on a Friday and the bus departure time is before the Dhuhr adhan?

It is permissible to travel on Friday before Zawāl (midday) according to the majority of scholars, but it is more cautious to avoid it to steer clear of disagreement. If the time for Jumu’ah (Friday prayer) has begun while you are in the city, it is not permissible to travel except for an excuse, such as fear of missing one's companions. If it is permissible to skip Jumu’ah, you pray Dhuhr (noon prayer). If you pray Dhuhr after leaving the city and passing its houses, you pray it shortened (qaṣran), i.e., two rakʿahs, and you are allowed to combine Dhuhr and ʿAṣr (afternoon prayer), and Maghrib (sunset prayer) and ʿIshāʾ (night prayer).