If using the factory Nav, you CANNOT mute the volume. Its a feature the Manual describes, but doesn't work. I cant use my phone for AA or Carplay due to being a company phone, so I have to use factory NAV, and basically its impossible to have it co-exist with the Stereo, due to constant interrupts from the Nav system. Its been a known issue for some-time.
One of the growing list of annoyances I've noticed after living with my Touring model for a year. With Honda's reputation for a buttery smooth user experience, many directly driver facing features are annoying. It's like they overthought some things and didn't even bother considering others.