Well yes, but using the tool he made you could argue that very few would deny it since the truth became so obvious. Even if it was known a long time before that, a lot of people still believed that the earth was flat.

With increased technology it was easily disproven.

Do you have a source for the claim that a lot of people believed the Earth was flat in Galileo's time? (Galileo was born decades after the Magellan-Elcano circumnavigation of the world.)

Sorry, it seems you are correct and I was wrong. I mixed up the idea of the geocentric model and thought the flat earth theory was included in that.

My bad and thanks for correcting and enlightning me :)