Concave earth is hands down my favorite conspiracy theory. The completeness of the lie is astonishing. I actually spent months trying to come up with a way to disprove it on a high-school-education only-trust-your-eyes shoestring budget, and couldn't come up with much.
This is a fun read on wikipeida [1]. I'm curious as to how you could disprove it at all: there's a perfectly valid coordinate transformation that maps our "infinity" to the center of the earth, and the center of the earth to infinity. All the laws of physics become position-dependent, of course, and it's not a convenient space for calculations, but it "proves" that the concave earth is a perfectly valid way of describing the universe.
I don't understand the difference the entry makes between the fact that you can represent the universe in a CHE model using coordinate transformations and "hypotheses". Given that you started from a concave model of the universe and the associated physical laws, you could make reasonable hypotheses and verify them through experimentation.
The most visible point I've seen is that the seasonal star constellations you know well (Orion in my case) will be seen as inverted if you change the hemisphere. The moon and sun position also change greatly. I'm not aware of any ideas that incorporate this.
It takes either time or money to see for yourself though.