Re-enable startup chime on new Mac
It's not possible.
From OSXDaily Where’s the Startup Boot Sound on New iMac &amp; MacBook Pro?

One theory promoted online and originating from some web forums was
that you could re-enable the Mac startup chime sound effect by turning
to the command line. The claim was that by launching Terminal app and
entering the following command syntax:
sudo nvram BootAudio=%01

And another variation which you see online are the two:
Disable the startup chime:
sudo nvram BootAudio=%00

Enable the startup chime:
sudo nvram BootAudio=%0

Supposedly, after executing that properly, the startup chime would be
enabled on the Mac again.
But it turns out that nobody bothered to actually test this out,
because it does not work.