No sound device for input or output after installing Ben Sur OS

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Before installing Ben Sur OS I had ensured I had a successful Backup to my TimeMachine.

Even went further by physically copying root directory files to the NAS backup folder.

Installation of the Ben Sur progressed with no error warnings*, except discovering the absence of a sound device once newly booted into the OS.

Sound is available for Sound Effects, Siri, Music app and FaceTime.

However, any applications that require a sound device (output or input) produces no sound.

e.g. Watching Twitch app has no sound, YouTube within a browser - no sound, recording using Quicktime has no sound.

Tried to no avail the following:

Asked Siri to unmute speakers
Restarted Ben Sur OS
Using Migration Tool: Restore to TimeMachine (before installation date)
Reboot holding ⌥ + R expecting to be able Re-install Catalina OS (only Ben Sur option available)

*Only other oddity was finding mixed/jumbled text in Chrome; this was fixed by removing and re-installing the Roboto font.

Where can I download the Catalina OS? (I have, so far, only been able to find updates - I don't see it in the App Store)
I thought restoring to TimeMachine, would include when it was Catalina? Seems not the case, could you confirm?
Any other advice welcomed to downgrade from Ben Sur OS back to Catalina OS.

Here is my MBP spec:

MacBook Pro Retina

Posted on Nov 18, 2020 6:14 PM

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Answer 1

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So I now write from having successfully rebuilt my MacOS back to CatalinaOS from Ben Sur.

The process that did work for me was to create a bootable USB with a copy of Catalina OS on it.

In order to do this you need a copy of CatalinaOS (source: https://www.macworld.co.uk/how-to/downgrade-macos-3581872/)
You could install a new copy of the OS without formatting the drive but this may take up drive space you may not have enough space on during the process of recovery.
I opted to format the drive.

After getting back into CatalinaOS, I was able to restore my content using the Migration Tool from my TimeMachine backups.

Hint: I got a little confused about what to select when formatting my drive, this article helps: https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/mac

I hope to see a fix appear in any upcoming updates to Ben Sur to address this issue; until then I'll hold upgrading.

If you have better luck with upgrading from CatalinaOS to Ben Sur on a MBP mid-2015 without losing your sound card do please share.

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