MacBook Pro M3 Max mic not working with FaceTime/Phone

I cannot get my built-in microphone to work with FaceTime nor the Phone app on my Macbook Pro M3 Max.

This issue occurs on this Macbook Pro, which started this morning on MacOS 26.3.1(a) and is now on MacOS 26.4. With both MacOS versions, the built-in mic shows working properly when viewing the "Sound" control setting, and the microphone works on Zoom, WhatsApp, Google Meet (via Firefox browser) and other video conferencing apps. I cannot get the microphone to function on FaceTime or Phone. Notably when the Facetime or Phone apps are open and I'm connected to a call, the small window in the top-right of the Mac shows no audio on the "meter" but if I open the control panel Sound setting window, one can see the volume bar picking up voice audio. This shows that the mic is working but not routing into either Facetime or Phone apps.

I first noted this issue earlier today (MacOS 26.3.1(a) when attempting to take a phone call from my Mac. I then updated to MacOS 26.4 with the hopes that it was an interim bug, however, am still experiencing the problem.

For diagnostics, I checked "system profile" via the terminal window. This is the report:

Audio:

Devices:

DELL U4025QW:

Default Output Device: Yes

Manufacturer: DEL

Output Channels: 2

Current SampleRate: 48000

Transport: DisplayPort

Output Source: Default

DavidPhone Microphone:

Input Channels: 1

Manufacturer: Apple Inc.

Current SampleRate: 48000

Transport: Unknown

Input Source: Default

MacBook Pro Microphone:

Default Input Device: Yes

Input Channels: 1

Manufacturer: Apple Inc.

Current SampleRate: 48000

Transport: Built-in

Input Source: MacBook Pro Microphone

MacBook Pro Speakers:

Default System Output Device: Yes

Manufacturer: Apple Inc.

Output Channels: 2

Current SampleRate: 48000

Transport: Built-in

Output Source: MacBook Pro Speakers

Microsoft Teams Audio:

Input Channels: 1

Manufacturer: Microsoft Corp.

Output Channels: 1

Current SampleRate: 48000

Transport: Virtual

Input Source: Microsoft Teams Audio Device

Output Source: Microsoft Teams Audio Device

ZoomAudioDevice:

Input Channels: 2

Manufacturer: zoom.us

Output Channels: 2

Current SampleRate: 48000

Transport: Virtual

Input Source: Default

Output Source: Default

I attempted to reboot while the Macbook Pro was disconnected from my external Dell monitor but had the same issue. This appears to have nothing to do with the use of an external monitor.

Notably, I also own a Macbook Air. I tested my Macbook Air while on MacOS 26.3 and it functioned perfectly. I was able to receive iPhone calls on the Macbook Air and use FaceTime without any issue. I updated my Macbook Air to MacOS 26.4 and it continues to work as expected.

I don't see any apps on my Pro that should be getting in the way. Both my Pro and Air have reasonably clean installs and not a ton of non-core apps. My Air has Logic Pro (I use it for music) and my Pro has X-Plane flight simulator. But otherwise, they're very similar setups.

Claude was of no help. I appreciate some human tips. This is frustrating as the Macbook Pro is my primary computer which I use almost every day for work and life.

Many thanks.

-- David