When I want to expand my soundtrack, I position the cursor on the upper track limit, maintain mouse click
and move up the mouse, as I do for windows size.
When I need more space, I can reduce the viewing global window of the project.
Unless you have the timeline set wider for Expert view and you're seeing a change of size when switching from Quick to Expert view, I know of no "toggle" for changing the track width with a single click.
Just as JM points out, in the Track's Header, if you hover the mouse above the upper boundry of that Track Header, the Cursor will change to an equal sign w/ up/down arrowheads, and if you click+drag there, you can expand, or contract the Track. The secret is watching the Cursor, to know when you are over the "hot-spot." It is a bit of a "pixel-hunt" the first few times you do it, but soon it will become second nature, and you will just naturally hit that spot.
When I first picked up PrE (had used PrPro for years), one of my first questions here was "where is the vertical Track expander in PrE?" It was slightly different in location, between the two programs - similar, but I just could not find that hot-spot. Well, the helpful people here, told me to just be patient, and hover the Cursor, as it WAS there, and they were correct. It just took me a bit to find it.
You nailed it. I just go to the timeline audiotrack I want to work with and put the cursor right above the word "audio1" or "narration", whereupon a little equals sign appears which I can then use to expand the audio display vertically. It works quite well. Thanks for such a prompt and useful response.
You are most welcome.
After you have found it a few times, you will wonder how you missed it before - I know that I did.