No startup chime

Please see: Turn the Mac startup sound on or off - Apple Support

Also, PRAM reset is as you noted: Command-Option-P-R (⌘⌥PR).

However, if you are using a wireless keyboard, the Mac may not boot the drivers for it quickly enough to register the keystrokes. You may need to attempt this with a USB keyboard.

Follow up:

You might try these commands in the Terminal app. They work for me on a Catalina Mac.

Copy and paste in to the Terminal app window.

To enable the startup chime:

sudo nvram StartupMute=%00

You will be asked to enter your admin password. (It will not display on the screen.)

To disable the startup chime:

sudo nvram StartupMute=%01

You will be asked to enter your admin password. (It will not display on the screen.)

This has been reported by some in the past. It also happened to me. The start up chime just stopped. Did not return until I updated the OS to the next level.

I tried these commands in the past and no luck unfortunately. But always worth a try. Only an OS update returned the function.