After update to the latest Mac Big Sur: Internal speaker bug

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation. The Built-in Security of Big Sur is all that is required.

Any of the above outline - may have interfered with the OS to the point of experiencing your issue.

And agree with @Luis S - run the Etrecheck application

Suggest downloading the Application Etrecheck directly from a Well Respected ASC Contributor. The application is free or paid from added features. Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ). It will take a Snap Shot -  both the hardware and software. The Report will Not Reveal Any Personal Information. Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Try P. Phillips's suggestion. Safe Mode only loads essential things, and also clears stuff like caches.

If things work ok in Safe Mode, restart normally and see if the problem was fixed.

If the problem is still present, please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

Reset NVRAM.

Also, if the issue persists, login as guest and see if shows the same problem there.

Have you tried Safe Mode ?? Does it present the same issue in that mode ( Safe Mode ). It will eliminate all third party software, extensions and fonts from loading.