NVDA won't tell you what combinations of fn key plus another key do and I don't know if the commands are carried out when you issue the commands when in the key describer.  Since fn keys in combination with other keys never announce what action is being taken either with  input help on or off and since what they do varies from computer to computer, I think it is a very bad idea to experiment with them.  You need specific information about your computer.
Does input help describe keys like audio commands?  Of course, it describes standard keys and commands but I don't have commands such as audio commands on keyboards I use.
Gene
-----Original Message----- From: Quentin Christensen
Sent: Friday, January 15, 2021 1:17 AM
To: nvda@nvda.groups.io
Subject: Re: [nvda] muting
Fn is a key found on most laptops and some desktop keyboards - it's basically a modifier key you hold down and press another key to perform an action (which a full size desktop computer probably has either a key or a button for).  The most common is the F1 - F12 function keys often perform other duties such as adjusting brightness, volume or disabling a trackpad mouse on a laptop.  On some keyboards you actually have to press Fn+function key to perform the regular function, which is frustrating - you can normally toggle that, but exactly how varies from keyboard to keyboard.
In terms of figuring out what keys do, if you press NVDA+1 (the 1 on the number row, above q) it puts NVDA in Input Help mode.  Any key you press while in this mode won't do anything, but NVDA will tell you what it is, so it can be a way to find your way around a new keyboard without sighted help.
If you normally use F7 to mute NVDA, that's not an NVDA keystroke, but it's likely that is the key to mute your computer's sound.  The keystroke to mute NVDA is NVDA+s, but if F7 works, that's achieves what you need.  If it's not working right now, it might be that you've accidentally toggled your function key Fn lock.
On Fri, Jan 15, 2021 at 5:55 PM Neil Campbell <nrcampbell@...> wrote:
Hello Brian
I have used F7 to toggle speech off and on before, but did not turn it off with F7 on this occasion, and F7 would not turn it back on.  What is “Fn”? I have a new keyboard which came with a new desk top computer, and there are additional keys which I don’t know the function of.  I will have to get a sighted person to tell me what they are.
Neil
From: nvda@nvda.groups.io [mailto:nvda@nvda.groups.io] On Behalf Of Brian Vogel
Sent: Monday, 11 January 2021 2:45 AM
To: nvda@nvda.groups.io
Subject: Re: [nvda] muting
Neil,
         Mute is typically done through a dedicated key on some media keyboards, or through F6 or F7 (when used as media keys) on many laptops and some desktop keyboards.  All it takes to trigger a mute by accident is Fn+F6 (or F7) and often Fn+F6 (or F7) will toggle it back off.
          This is another of those instances where make and model information as well as whether any media keys function is enabled (and for a screen reader user I'd very, very strongly suspect it's not unless the machine is brand new and untweaked yet).  Some makers do highly unconventional things as far as what function keys correspond to what media functions.
           Gene's advice about using sndvol and getting a cheap external USB soundcard are both things to try and do.