How do I check the active audio codec for a bluetooth connection in Big Sur?

How do I check the active audio codec for a bluetooth connection in Bug Sur?

In Catalina, you used to be able to option-click on the Bluetooth item in the menubar, and then it would show more detail about every item including the codecs for audio devices. Now it still shows the additional detail but not the audio codec.

How do I see the audio codec being used now -- for instance, to ensure that my headphones are using AAC and not SBC?

Download Bluetooth Explorer, open it, then navigate to Tools > Audio Graphs. You can see at the bottom the active codec - in this example I'm using AAC.

Note that Bluetooth Explorer is no longer included in the latest Xcode Additional Tools bundle. The last version I could find was for Xcode 11, and it now crashes sometimes on Big Sur, but still does the trick. Download it here: https://developer.apple.com/download/more/?=additional%20tools