I have read a lot of pieces and seen a lot of “news” about this mythical continent of Zealandia. And they are all wrong. If the two islands of New Zealand were on a submerged continent you would think that would make them on the same piece of Rock, and they aren’t.
The north island is on the Indo Australian plate, the south island on the Pacific plate. And the two islands are purely the result of their part of the plate subducting the other plate just like Indonesia and PNG on the northern plate boundary. The side being subducted causes the other side to rise and also causes volcanoes on the side that is rising. The two islands are the result of this colision and subduction and volcanoes, nothing else. If the pacific plate had all subducted under the Indo Australia plate along this boundary the so called continent would not be there at all.
Note that at the point the fault crosses the top of the north island that the pacific side has a clear line of the area that has uplifted and is building undersea shelf higher. This no long lost continent but the result of normal tectonic action and mountain building.