I have been to the modern city of Tyre myself. I have also walked the ruins of Tyre–or more accurately the Tyre of the Roman period. Tyre was destroyed and “scraped into the Sea” by Alexander the Great.
Yes, these ruins are the ancient city of Tyre. However, the question is a bit complicated. Ancient Tyre in the period of the Babylonians and the Greeks consisted of a mainland city, with a smaller protected part of the city built on an island off the mainland. The part of Tyre that was off the coast was completely destroyed by Alexander in 332 BC. At that time he built a massive causeway to the island in order to conquer it. When the island was taken, Alexander had his troops scrape all vestiges of the island city into the sea. These ruins are for all practical purposes gone, but the island and its causeway have now become a peninsula. When archaeologists excavate the city of Tyre it is the version from the Roman period, which is on the mainland, with the more ancient mainland ruins below that. It is not accurate to say that Tyre is a “sunken city.” There is a tiny grain of truth in this label because much of the island city of Tyre was scraped into the sea. The site of the city is not underwater, but some of the material that formed the city is under the sea. In modern times, the peninsula has been reoccupied. It is dominated by the Hezbollah Shia Muslim sect. The reason scholars are confident that the current city known as Tyre is on the site of the ancient city is that we have the reports of historians such as Herodotus from as early as the 5th century BC who visited the city and described it. The site was nearly abandoned during the Middle Ages, but knowledge of the island-turned peninsula of Tyre has never been lost.