why is there no sound on my Imac after Catalina?

Hi astrid104

I recall the same issue after a Catalina update.

Are you using the internal Mac speakers for sound or are you using external Bluetooth speakers, or a set of speakers plugged into the headphones socket on the back of the Mac?

First place to check is in System Preferences > Sound > Output tab

Check the speakers you are using are selected in the list of devices.

If you have multiple devices for sound available then select the internal Mac speakers, disconnect any external speakers that are plugged into the headphone socket at the back of the Mac and at the bottom of the Output tab make sure that the "Mute" button is deselected and adjust the volume slider to the right.

After verifying the above do you hear sound now when you play a sound source?

If yes, but you want to use Bluetooth speakers, are the Bluetooth speakers listed under the devices list?

If the Bluetooth speakers are missing from the list of devices then in System Preferences click on the Bluetooth settings icon and verify that your Bluetooth speakers are detected, if not found you may need to repeat the Bluetooth pairing procedure as described in the user manual for the Bluetooth speakers.

If the Mac internal speakers are selected, the speakers are unmuted, the volume slider is to the right, but still there is no sound then carry out a SMC and NVRAM reset as detailed in these two documents:

https://support.apple.com/en-us/HT201295

https://support.apple.com/en-us/HT204063

If sound is still not restored after the above steps then boot the Mac into Safe-Mode one time.

Booting into Safe-Mode is simple and requires no specialist knowledge, this procedure will reset several macOS "hidden" settings that affect many of the iMac components such as Sound, Video, Bluetooth, Wireless etc.

When booting into Safe-Mode there is no need to do anything other than startup the Mac in Safe-Mode, wait for the Safe-Mode boot to reach you user desktop, which takes up to ten minutes, wait a further ten minutes for all background processes to complete and then restart the Mac (Apple Logo, top-left of screen, select "Restart...").

After the restart the Mac will once again be in Normal-Mode and hopefully sound will be restored.

If, after all the above, in very rare cases the above procedures do not restore the Mac sound, then boot the Mac into Recovery-Mode and select the option to reinstall the macOS.

Re-installing the macOS in Recovery-Mode will download a fresh copy of your current macOS (Catalina) while keeping your apps and data intact, even so, you should have a Time Machine backup of your Mac before you attempt a re-install of the macOS, just in case the procedure fails and you need to recover your important apps and data after a full disk-wipe and "clean-Install" of the macOS.

This document details the key-combinations required to launch into Safe Mode and Recovery Mode:

https://support.apple.com/en-gb/HT201255

This document describes Safe-Mode in more detail:

https://support.apple.com/en-gb/HT201262

This document describes Recovery-Mode in more detail:

https://support.apple.com/en-gb/HT201314

One of the above steps should restore sound on your iMac.

HTH

Will.