In new GameMaker 2 update there are so many major changes: https://help.yoyogames.com/hc/en-us/articles/360011980018
We develop our game (https://store.steampowered.com/app/733460/First_Feudal/) on this engine for 3 years. There was no other way to handle state before: only arrays. No structures and model objects.
So we have really many arrays in our game. We use 1d and 2d arrays. From now GML have only 1d arrays, and 2d or other multidimensional arrays - are 1d array of 1d arrays.
For now after update from 2.2 to 2.3 GameMaker your arrays may work ok. But there are some issues. First of all some array functions will deprecate in next versions. And some of them (like array_height_2d) may work in different way if you mix 1d and 2d logic.
So, how to update 2d arrays to new 2.3 format, and don't use obsolete functions later?