Apple announces that hearing aid sound problems with iPhone 12 models will be resolved in a future software update.
Apple to fix a bug between MFi hearing aids and iPhone 12

In a support sheet, Apple acknowledges that some Made for iPhone hearing aids produce “abnormal” sounds with the new iPhone 12 (all four models are affected). This bug is rather annoying since it can cause very noisy noise, a mute or interruption of the sound, or a distortion of the sound.
The bad news being over, let’s move on to the good news: Apple is aware of the problem and will deliver a fix in a future iOS update. The salvation may come from iOS 14.3, available in the first beta since this week. Unless a maintenance version like iOS 14.0.x comes to the rescue for owners of this type of device.
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