I’ve just updated to High Sierra 10.13.6 so got the new Audacity 2.3.0. I had been far behind with Lion and an older version of Audacity. I’ve found that I have NO vertical zoom in the new version, which is quite annoying trying to edit, and nothing I do suggested in the manual on in the forum seems to enable it. Has anyone else had this problem? Please help.
Vertical zooming has changed.
You can go back to the old way by going to Preferences > Track Behaviours and checking “Advanced Vertical Zooming”.
The though behind this change is that we were getting many reports from users who had accidentally clicked in the vertical ruler and didn’t know what they had done or how to get back to normal.
– Bill
Whew…thanks a bunch, Bill. Tearing my hair out there for awhile and just wasn’t seeing it.
Unfortunately old zoom functionality has not been preserved exactly: right mouse-click used to zoom-out,
now it brings up the new zoom menu, which has “zoom-out” on it,
but you have to move the cursor to the “zoom-out” option on that menu, and click the mouse again. 
What was achieved with one mouse click now requires two mouse clicks, and moving the cursor to a menu option.
Logically when you tick “Advanced Vertical Zooming” should revert to the old method exactly, not this inefficient hybrid.
It’s very close.
You don’t. You can “Shift + Left Click”.
“Edit menu > Preferences > Tracks Behaviors → Advanced vertical zooming”
When enabled, you have:
Left Click = zoom in
Left Click + Drag = zoom in on dragged region
Shift + Left Click = zoom out
Shift + Right Click = Zoom normal
Shift + Mouse Wheel = scroll (unless zoomed in to max)
Ctrl + Mouse Wheel = Zoom
The new Right Click menu is in addition. Right click for a context menu is pretty standard across many applications.