Is this sarcasm? I genuinely can't tell.

The ancient Greeks came up with a pretty accurate estimate of the radius of the Earth just by looking at ships disappearing over the horizon. Literally anyone with even a cursory knowledge of geometry can prove its general shape. No one in science has any doubt. Zero.

The bigger question is why anyone would deliberately claim the Earth isn't flat if it actually was. What benefit does that have? What lobby is behind the scenes keeping it a secret exactly?

Also, linear infrastructure beyond a certain size explicitly has to account for the curvature of the Earth. Long bridges have the pillars slightly offset from parallel and that offset needs to be constantly measured during construction to ensure it's correct. High speed train viaducts have to be slightly curved to follow the shape of the Earth. Ships still use nautical miles because it specifically accounts for the curvature while SI units and regular miles are defined as straight lines only. Line of sight radio systems like microwave dishes don't work past a certain distance because it's impossible to get line of sight with the Earth in the way, necessitating repeater towers that break up the straight line into a chain of antennas that can change the beam direction, and the angles of the antennas are calculated to account for the shape of the Earth. Same with FM radio towers whose coverage is limited by the horizon. Same for radar. If the Earth was actually flat all along, why would we have to take curvature into account when it would have saved private trillionaire corporations who do control our world untold time and money to not pretend it's round?

Finally, why is the Southern Cross only visible in the southern hemisphere? If the Earth was flat shouldn't we be able to see all the stars from any perspective?