Apple - Is there a shortcut to expand all folders in Finder's list view?

Select the folder you want (or command + A to select all) and then press:

• Command + right arrow

And the left arrow undoes what the right arrow did, should you want to close things back up again.

I find mouse/trackpad-clicking the triangle while holding the Alt/Option or Command key works too.

To expand one single level folder

Command Right arrow

To expand all levels of subfolders under the selected folder.

Command Option Right arrow

OR

Option and click the triangle in folder view in Finder