Just to clarify,
If you are on Windows 10, the OS supports bottom, left, top, and right taskbars. It is not a function of Start11. However, if you use the enhanced taskbar of Start11, it does not support left or right taskbars, but does support top and bottom taskbars.
If you are on Windows 11, the OS only supports bottom taskbars. The Start11 enhanced taskbar supports top and bottom taskbars.
So the answer is yes to left taskbar if you are on Windows 10, and no if you are on Windows 11.