Apple has published a support document outlining steps to try if the Apple Watch's microphone or speaker is not working properly.
The potential solutions listed include updating the Apple Watch to the latest watchOS version, restarting the device, un-pairing and re-pairing it to an iPhone, checking Silent Mode and Do Not Disturb settings, cleaning the microphone and speaker, and drying the device.
These steps are also recommended if the audio from the Apple Watch speaker is crackling, distorted, muffled, or intermittent.
Apple has not officially commented on the reported Apple Watch Series 10 speaker issue, but this support document provides possible interim solutions while the matter is investigated.