This message was posted on behalf of Intel Corporation
We understand your concern related to the Intel® Dual Band Wireless-AC 3168.
We would like to let you know that the channel width when is set up to auto is going to be controlled by the router. If your Router does not support 40MHz or 80MHz the adapter is going to use the width it is able to handle.
If you set up the width to 40MHz or 80MHz and the Router does not support it, you would have some issues related to the width and connection rate.
That is why there is not an option for you to select the channel width on the adapter only to limited to 20MHz or leave it out to the Router to choose the width.