Can't "Unmute" in RealVNC Connect 8 (r189)

When connecting to a RealVNC server using RealVNC Connect 8, the audio icon says "unmute" when hovering over it, but clicking on it does nothing.  As a result, audio is not working on the client.

• Both the client and server are running fully updated Windows 11 Pro
• Both the client and server are running RealVNC Connect 8 (r189)

The only documentation I've found is outdated and doesn't reflect RealVNC Connect 8 (r189):
https://help.realvnc.com/hc/en-us/articles/360002504358-Audio-in-RealVNC-Connect#how-do-i-turn-the-audio-feature-on-or-off--0-2

What steps can I take to enable audio?