Loss of sound on 2020 Intel MacBook pro

installed with Ventura.

was watching you tube video using internal speakers then sound cut out when an advert came on. The sound didn’t come back. Tried resetting vram and smc etc, internal speakers still selected in settings. Occasionally get the bong back after reset and the sound was present initially with Apple TV, but disappears again after a few seconds. Tried closing coreaudio and didn’t seem to make any difference. Not seen coreaudio since to try closing it again. Reinstalled the operating system, same problem. Can’t revert to a previous operating system as no Time Machine backup. Occasionally these steps will bring sound back for a few seconds, but not for long. It’s as if something isn’t compatible and kills the sound. Any ideas?

thanks