It is my understanding that most flat earth models have the sun/moon/stars rotating in the sky above the flat plane of the earth.
I've thought of the perfect test to debunk this, and while it doesn't prove the earth is round per se, it does definitively prove that celestial objects are traveling under and around the earth, not merely circling above it.
I implore any flat earthers out there with a modest budget to invest in a cheap EQ (equatorial mounted) telescope. Invest in one, you can probably get a cheap used one that's more than capable of doing the job for around $50. Perhaps you could borrow one from an astronomer friend or acquaintance.
Take an 30 minutes to 1 hour to learn the basics of how an equatorial mount works. Go in the back yard, properly set it up (adjust to your latitude, Polar align the scope), and train it on any celestial object, the moon, a star, a planet, preferably one that is further out from the celestial poles (The North Star Polaris for those of you in the northern hemisphere). Any planet should do. You can even do this on the sun (WITH A SOLAR FILTER!! DO NOT USE A TELESCOPE ON THE SUN WITHOUT PROPER PROTECTION)
Track the movement of the object through the night. You now only need to use the one right ascension control knob to track its movement as it travels through the heavens(Actually Space). Watch as it disappears over the horizon. Keep using the right ascension knob to project where the object goes into the future. The celestial object's path will take it directly underneath the earth.
The point of this experiment is debunk, for good, anyone who uses the nonsensical "perspective" argument. This is the easiest way to visually prove to yourself that objects aren't disappearing due to being too far away, but rather traveling underneath the earth, making a full circle around it, and coming back up on the other side.
I challenge any flat earther to accomplish this task and remain a flat earther. As I said this doesn't necessarily prove the earth is a sphere, but it does debunk any flat earth model I've ever seen. There is simply no flat earth explanation for it that exists.
Outside the bounds of the experiment, as an added bonus, once you do this experiment, train your new scope at Jupiter or Saturn. Watch as the planet obviously rotates on it's axis. Observe the moons as they transition in orbit around the parent planet. Watch the shadows they cast. Yes, you CAN see this.
I'm introducing you to the rabbit hole that is knowledge. I beg you to go down it.