Take any phenomena on a globe earth, describe the exact same thing in flat earth coordinates and then say that everything weird in the equations is a new physical effect you just discovered.
…which have other consequences that are easily disproven.
Flat earthers are empirical cosplayers. It mostly seems they just want something to argue about and couldn’t come up with anything original.
If every observation conspires to make it look round, it's round because observation is all we have. Refusing to accept observational evidence that forms a coherent explanation is either anti-science or anti-definition-of-words. This justification for flat earth exits the realm of scientific inquiry and enters the realm of Cartesian evil demons, a hypothesis even Descartes rejected.
You can't actually do that in an internally consistent way. (Or atleast I've never seen it.) It isn't only interally incosistent but those theories also break down if you look at them too closely. That's why so much of flat earthism relies on conspiracy theories that are used to justify ignoring phenomena rather than actually investigating it.