New AirPods, AirPods Pro, AirPods Max firmware updates are now available
As part of a wide update, Apple has issued new firmware revisions for AirPods, AirPods Max, AirPods Pro, Beats Solo Pro, Powerbeats 4, and Powerbeats Pro.

Expected in the update are Apple's standard performance improvements, and bug fixes. The update also brings support for Conversation Boost for the AirPods Pro.
Announced at Apple's worldwide Developers Conference in June, Conversation Boost leverages microphone beamforming and machine learning technology to isolate human voices. The feature is tuned to focus on a person speaking directly in front of a user, making it easier for AirPods Pro owners to listen during face-to-face conversations.
Conversation Boost can also filter out distracting ambient noise.
All devices get firmware version 4A400.
The new firmware is installed automatically for users, with no mechanism available to manually force an update. As long as AirPods or AirPods Pro are in a charging case and connected to an iOS device, the firmware will install by itself.
AirPods users can check the current firmware for their audio accessories within the Settings app, selecting General, then About, then select the relevant device from the menu.
Read on AppleInsider

Expected in the update are Apple's standard performance improvements, and bug fixes. The update also brings support for Conversation Boost for the AirPods Pro.
Announced at Apple's worldwide Developers Conference in June, Conversation Boost leverages microphone beamforming and machine learning technology to isolate human voices. The feature is tuned to focus on a person speaking directly in front of a user, making it easier for AirPods Pro owners to listen during face-to-face conversations.
Conversation Boost can also filter out distracting ambient noise.
All devices get firmware version 4A400.
The new firmware is installed automatically for users, with no mechanism available to manually force an update. As long as AirPods or AirPods Pro are in a charging case and connected to an iOS device, the firmware will install by itself.
AirPods users can check the current firmware for their audio accessories within the Settings app, selecting General, then About, then select the relevant device from the menu.
Read on AppleInsider
Comments
Actually...
To check your AirPods firmware version:
And I found nothing under Settings in General, but did under Bluetooth. So thanks poster Spitbath for that tip.
Now for my various AirPods, which are currently at 3E751.
You are right, although the method mentioned in the article only shows the AirPods if they are currently connected. The other method lists all bluetooth devices no matter what their connection status is.
edit: I found the setting, if anyone cares…
1)Accessibility
2)AirPods
3)Audio Accessibility Settings
4)Headphone Accommodations
6)Conversation Boost (toggle is near the bottom of the screen…turn on)
Now you can quickly access it along with a few extra new features under the Hearing button in the Control Center, including the ability to adjust Transparency Mode Amplification on the fly without having to dig through the settings (finally!).
Hope this helps someone.
https://support.apple.com/en-us/HT209463
Anyway, my AirPods still hadn't updated, so I followed the procedure here which updated the AirPods Pro case from 1.0.8 to 1.3.5 and the AirPods Pro to 4A400.
https://www.iphonetricks.org/airpods-firmware-4a400-update-how-to/