Should the 30th day of Ramadan be made up if one Arab country declares it the first day of Eid al-Fitr based on astronomical calculations, while neighboring Islamic countries continue to fast?

It is not permissible to fast or break the fast based on astronomical calculations. If you know that a country relies on this, do not follow it. Instead, fast based on the sighting of the crescent moon, or based on the sighting in the nearest country that relies on the crescent moon sighting. And whoever broke their fast merely based on astronomical calculations and the neighboring countries that were fasting, they must make up that day, and there is no sin upon them if they were ignorant of the ruling.