Try running the Apple Diagnostics to see if any hardware issues are detected.
Try creating a new macOS user account. Log out of your main user account and log into the new user account. If the audio is working, then you have some sort of configuration issue with the main user account or possibly a corrupt .plist preference file.
If you have 80+ GB of Free storage space (ignore the "Available" space value as it is very misleading), then you can try creating a new APFS volume & installing macOS to that new volume (minimal risk). See whether the audio is now working.
- Do not restore from a backup.
- Do not install any third party apps
- Do not log into your AppleID or iCloud.
Test the fresh macOS installation with just a clean install. If this works, then you can try reinstalling macOS over top of itself on the original OS installation (it should not affect your apps or data). Otherwise you may have a system configuration issue or a corrupt .plist system preference file. Before deleting the new APFS volume after you are finished testing, make sure to boot back into your main OS volume and reselecting the default Startup Disk for the original boot volume. Deleting the new APFS volume without changing the default Startup Disk back to the original boot volume may cause some boot issues & may be a bit tricky to resolve depending on your system configuration.
You may also want to try a DFU firmware Revive which resets the security enclave & system firmware. This should not affect any data on the internal SSD, but if the process fails to complete successfully it could leave the system in an unknown state where it may be impossible to access the data on the internal SSD.
Before doing anything make sure you have a good current backup just to be safe in case something goes wrong. I hope you already have frequent & regular backups since there are a lot of new ways to permanently lose access to the data on the internal SSD due to all the hardware, software, and security changes.
