The encircling icy landmass is a pretty easy one to prove. Millions of people have circumnavigated the earth east to west. Obviously I think they are making a circle around the north pole on our plane. No one has ever circumnavigated across the south pole and come out the other side of earth. A flight from Perth AU to Buenos Aires would have the shortest path across the middle of Antarctica. But try it yourself and watch what flight routes come up when you book it; it makes perfect sense on a FE map. https://youtu.be/WOl3uf2SeNU

Have you seen any of the vids of ships disappearing over the horizon from the bottom up, then they use a nikon p1000 to zoom in and bring it back into full view? It's just an optical effect. Besides ships over the horizon is kind of irrelevant when people view objects all the time that should be hidden behind the earth curve such as lighthouses, islands, mountains, skyscrapers. And the military has targeting systems (lasers) that target objects a couple hundred miles beyond what should be possible geometrically. Here is an observation I made myself that should be impossible, message me privately if you want more specifics on the sighting. https://communities.win/c/flatearthresearch/p/16ZXQp6ItT/flat-earth-observation-san-cleme/c

The sun is the most difficult one because there is so much unproven about it. How big is it? how high? does the firmament effect its light distribution? Does it have a physical location, or is it some sort of projection that depends upon the observer? I don't know for sure and it was the hardest thing to explain about FE. How can you possibly experience night if the sun is moving over a plane? I was convinced by watching many videos that offered demonstrations and simulations. Here is a playlist, that's the best I can do. https://youtube.com/playlist?list=PLyHwsN1Rg4IqA_ZqjXvtHsjLlksN_CS8u