Do you need to own an iPhone to use Siri on Mac?

Now also check your sound settings to make sure the MacBook can hear you.

System Preferences > Sound > Input

Make sure the Internal Microphone is selected. Set the volume slider appropriately and see that the sound level bar reacts to your voice.

If that all seems to be correct and working but you still get no response,  see if the problem still happens in Safe mode (hold the shift key down at startup). It can take much longer (10 min) to safe boot so be patient.

How to use safe mode on your Mac - Apple Support 

Safe mode forces the OS to clear certain caches and logs and do other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's normal.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and re-evaluate the issue again.

How to use Siri on your Mac

Also, Profile showing MacBook Pro 13″, macOS 11.2 this is out dated. The present version of Big Sur is now 11.5.1. Suggest doing a Time Machine Backup Before attempting the updates.

No, you don't need to own an iPhone to use Siri on the Mac.

But you do need to make sure Siri is enabled in System Preferences > Siri.

Use Siri on your Mac - Apple Support:

https://support.apple.com/guide/mac-help/use-siri-on-your-mac-mchl6b029310/10.13/mac/10.13

Good advise from pervious person posting and suggest following.

If this is the new Apple Silicon M CPU the Safe Mode is different that Intel and that too is covered in link supplied by @ D.I Johnson

Apple silicon

1. Shut down your Mac.
2. Turn on your Mac and continue to press and hold the power button until you see the startup options window.
3. Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode.”
4. Log in to your Mac. You might be asked to log in again.

What is not working and in what way is it not working. Enable " Show Siri in Menu Bar " is only thing not enabled.

Good and thank you for the update