Ferdinand Magellan proved that the Earth is round give reason
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༺ศསຮཡཛཞ༻
He didn’t.
It was well known by the Ancient Greek philosophers by observations made in Southern Europe and Northern Europe that the surface of the Earth was at least hemispherical, and combined with evidence gathered by Phoenicians when they circumnavigated Africa that the Earth was almost certainly spherical.
Eratosthenes (300BC) was able to calculate the circumference of the Earth to within 5% of the current accepted value - quite remarkable when you consider he used a stick, a well and manually measured distance between two cities.
By the time of Magellan, evidence from across Africa and Asia proved that every part of the Earth exhibited the same evidence of being on a spherical surface, and the case was proven.
What Magellan proved that there was a route around the Earth - It was known that you could sail from Europe, southwards around Africa and then East to China & Japan. It was known that there was a large body of water East of Asia (i.e. the Pacific) and there was land west of Europe - i.e. Greenland much of the coast of Western North America had been mapped, and South America had been discovered and the Northern Brazilian coast had been mapped too.
Magellan guessed (and was proved right) that the Atlantic and Pacific were connected by at least one passage of water at the very south of South America - he did nothing to prove the total extent of South American continent, or map the coast south of Brazil, or even whether that were any other connections, although we know that there are none (or at least none that are sensibly passable).
Magellan’s journey - South West across the Atlantic, south of South America, across the Pacific in an approximately north-westerly direction and then traveling west, to the south of India, and then around the south of Africa and North to Europe, would have entirely possible on a flat Earth (with the North Pole at the center of the disk); although within the records of his estimated position and timings that he made his journey, those made in the Southern Hemisphere would have been awfully inaccurate if he had been sailing on a flat disk