I guess I should say, with different laws of geophysics.

A different universe, huh?

Let's see! A planet, formed by some means "impossible" in
this universe, becomes a flat disk-like body.
The physics, including geophysics would be different, but not
completely different: such a universe may still have gravity,
but not the inverse square law of gravity perhaps.
And there would be elements like iron and they may dominate,
instead of hydrogen and helium. Iron in such a universe
may be much more common than silicon or magnesium, aluminum, oxygen.
And hydrogen would be as rare as copper or zinc in this universe....

And there would be a different dynamic causing stellar illumination
in such a universe; perhaps by matter-antimatter annihilation.
And how would such a universe keep from collapsing quickly?
By hitherto unknown laws of physics [unknown and impossible
in this universe]

OK! The flat-Earth in such a different universe....Well...It
may have a literal solid steel or iron disk core....

And poor old "different" universe Ferdinand Magellan.
[his different universe Doppelganger] He and his ship
went over the edge into...into?...Let your imagination
run wild.