OK, I'll play along. Here's a small selection of the most obvious round earth evidence.

• It looks round. There's a horizon and objects disappear behind it bottom first. On a flat earth, we should be seeing distant objects tens and hundreds of miles away. We don't. The curve can be confirmed to exist using lasers, flat earthers have tried and failed to debunk it. If you think the earth is flat, what should a round Earth look like?
• We can predict the movement of celestial bodies (all of them round) perfectly using the heliocentric round earth model. Sun angles, sunrise and sunset times, same for the Moon, all predictable to the second all over the planet all year round. Flat earth model says they, uh, move around up there.
• We understand why it's nighttime in Asia while it's the afternoon in America and morning in Europe. Impossible on a flat earth, can't illuminate part of a flat plane with a point light source, it will all be lit all of the time.
• We can understand and predict different phenomena: lower sun angles and larger day length variation further from the equator all the way up to white nights, polar night and midnight sun near the poles. Midnight sun in the north while it's polar night in the south. I live in the north and I'm experiencing it now. Completely impossible to explain with a flat earth.
• Seasons. Opposite seasons on opposite sides of the earth. No real seasons near the equator. All perfectly understood, explained and predicted.
• Satellites and GPS. Orbital mechanics are well understood, I've worked in the industry. Low orbit satellites move in a perfectly controlled and predictable manner, communication windows depend on line of sight based on a round earth model. It's real and it works. Impossible on a flat earth.
• Tides. Again, perfectly understood, explained and predicted, impossible on a flat earth.
• Rotation of the earth. 15° every hour, easy to confirm with gyroscopes. Flat earthers tried and failed to debunk it.
• Plane traffic. Many connecting flights in the southern hemisphere would be out of the range of current passenger planes. They aren't.

But hey, let's ignore all that because a neckbeard in a 360p youtube video told me we're being lied to and the field outside my house looks flat. The only thing flat earth theory can prove is that the Dunning-Kruger effect is real.