Juli Clover, MacRumors:

According to Apple’s developer website, the second ‌AirPods Pro‌ firmware update adds support for Conversation Boost, a feature that was missing from the first beta.

Conversation Boost is an iOS 15 feature that uses the beamforming microphones in the ‌AirPods Pro‌ to boost the volume level of conversations, which is ideal for those with mild to moderate hearing challenges.

Think about being in a crowded, noisy restaurant, with a lot of bouncy surfaces and multiple people talking at once. Conversation Boost uses computational audio to focus on and amplify the sounds coming from the direction in which you are facing.

The video embedded below (from back in June) does a nice job showing this.