Let’s take this “Back to the basics” question and test things out.
So, we have this 20 MHz capable Windows 11 Wi-Fi client and we want to see what happens when it attempts to join an SSID that uses 80 MHz wide channel. Will it associate? Will it fail?
Here is my client with Intel AX201 adapter forced to only support 20 MHz wide 5 GHz channel.
My AP uses 80 MHz channel width.
Let’s verify the settings from a Mac. Yes, the AP broadcasts 80 MHz wide “lab5” SSID with primary channel 36.
Finally, what happens if the client device is only capable of 20 MHz channel width? As you can see, it will happily join using Primary channel 36.
More capable client devices that support 80 MHz channel width will benefit from the 4 bonded channels and use the 80 MHz channel in its entirety.