What is the ruling on the demolition of Islamic antiquities that occurred in Saudi Arabia, and is there any legitimate justification for that?

The Muslim ruler must remove traces that are feared to affect the beliefs of the common people and their extremism, as a preventive measure, just as Umar (may Allah be pleased with him) did when he was informed that some people were going to the tree of the Pledge of Ridwan, so he ordered it to be cut down. Similarly, Ali (may Allah be pleased with him) ordered the leveling of elevated graves to protect people's beliefs from extremism, innovations, and superstitions.

As for traces that are not feared to harm the beliefs of Muslims, they should not be removed. Rather, it is better to leave them for contemplation and to remember the stories of the righteous predecessors, unless there is a reason for their removal, such as expanding a road or a mosque.