A diamagnetic material.

"In simple terms, diamagnetic materials are substances that are usually repelled by a magnetic field. Electrons in an atom revolve around the nucleus, and thus possess orbital angular momentum. The resultant magnetic momentum in an atom of the diamagnetic material is zero."

Am I correct in my understanding that being capable of self-levitation would be an unusually strong example of the diamagnetic effect?

Yes, if this material is diamagnetic without being a superconductor it is by far the strongest such material we've ever found. 15x stronger than pyrolitic graphite.

From what I heard, it would. This kind of diamagnetism would be strong enough to be potentially interesting in other applications and research, if it turns out not to be a superconductor.

Would still be useful for maglev, I assume?

Not over a single dipole magnet. The "shape" of the field wouldn't make it stable, you'd need to add other magnets or a piece of string to stabilise. As I understand stable levitation over a dipole magnet is indicative of flux pinning which is a property exclusive to type II superconductors.

I think ChatGPT wrote that because it is nonsense.

It came from here... correct or incorrect.

https://byjus.com/jee/diamagnetic-materials/

The Meissner effect requires a temperature transition in the diamagnetic behaviour. As you increase the temperature, you would expect a sharp drop with the material falling back on the magnet, and then levitating again once the temperature drops.

Yes, if you know the upper boundary for the temperature up to which the material stays superconducting. But that's a bit of a problem: this material is claimed to be superconducting to very high temperatures. It just could be that it isn't all that easy to reach a temperature where this stuff stops being superconducting. In fact I see no particular reason in physics why it would have to stay below the temperature at which the material disintegrates. So maybe that part of the effects is simply a reflection of the fact that these superconductors that work well below zero are in fact exactly there because they require a cold environment and once you find one that doesn't that whole aspect goes away, it could stay diamagnetic all the way up to its melting point.