What should a Muslim do if the date of Eid al-Fitr differs between the country where they are present at the time of moon sighting and the country to which they will return before Maghrib, and what is the ruling on their intention to fast this day with the intention of making up (qadaa') if it is the thirtieth day of Ramadan, or to take the traveler's concession if it is the day of Eid?

You should break your fast upon sighting the crescent moon in the country where it was sighted, which is Saudi Arabia. You did well by breaking your fast as mentioned, and you do not need to make up that day, because you broke your fast based on a legitimate sighting. You fasted twenty-nine days, and the difference in crescent moon sighting between countries is not problematic if there is a difference in the moon's rising places, as this is religiously permissible. A person's entry into Ramadan or its end depends on the country in which they commenced or concluded it.