The feature works, with a slight caveat. You press the [Alt] key, then start your vertical selection by dragging your mouse, or by holding [Alt-Shift] and clicking on another part of the code. BUT it needs a minor improvement to make it work more properly.

When you use [Alt-Shift], the behaviour is similar to other modern text and code editors. But when you just press [Alt] and start a mouse-drag, it also sets the application's focus to the menubar (for keyboard menu access). In order to start using vertical editing, you need to press [Alt] again so the menubar loses focus.

I would suggest that what should happen is when the user presses the [Alt] key and initiates a mouse-drag in the code area, the menubar should lose focus, so the user can engage in vertical editing.

Just a suggestion.

If this is already implemented then how do I turn this feature on? This isn't something that seems to work out of the box.

Lets say I want to append the same where clause to a bunch of select's at the same time if I hold shift+alt and use the arrows to select this will select things in the same way that just shift+arrows will. I can then press left or right arrow to select what appears to be a column selection. But if you start typing it cancels the selection and appends at the current cursor position instead

This isn't normally how an alt select works