Any fixes for persistent NO SOUND issue on 16" MBP (2020) OS 11.2…?
(Apologies if these seem redundant after all the support calls you’ve done...)

After erase &amp; reinstalling, did you check speakers before installing your audio apps?
Does Safe Mode (Shift during boot) help?
What is the output of ioreg -r -c AppleHDAEngineInput ; ioreg -r -c AppleHDAEngineOutput?
What audio devices have you been attaching to your system? (Wondering if something might be overdriving the input preamp past an absolute maximum rating...)

UPDATE:

Yes I did check speakers before migrating. They worked.

This is a very important piece of data - it rules out hardware as being at fault. So now we’re solely focusing on what pieces of software in your migration caused this regression.
We can do this a few ways:

Create a new user account, reboot, log in with the new account first, and check your audio. This won’t help unless the cause is a user-specific misconfiguration.
You can try uninstalling one audio app at a time. This won’t help if the uninstaller of the offending software doesn’t do a thorough cleanup.
Reformat and reinstall the OS but do not migrate. Instead, install your audio software, one app at a time, until you see the failure. This is the most reliable (and most time-consuming) path towards root cause.

The ioreg command requires Xcode to be installed. If you don’t want to install it (understandably so), you can download IOJones and use its filter bar to search for AppleHDAEngineInput and AppleHDAEngineOutput.