Interesting. On Windows 10, it shows a in/out "Headset (AirPods Hands-Free)" and an out only "Headphones (AirPods Audio)." So this transition would be very easy for the user to see. However, I've as yet been unable to get a straight answer on what profile the "Headphones" mode is actually using.
Apple products that implement AAC over A2DP only do so on iOS devices (and in only limited cases), and also do not implement anything else (such as any form of AptX, or LDAC).
you can tell macOS to use AAC using an Apple tool called "Bluetooth Explorer". Also, Macs equipped with a T2 chip default to using AAC even without the manual intervention.
You can check what codec is used by alt-clicking the bluetooth icon in your menu bar and hovering over your headphones. There will a an "Active Codec" entry that shows which one is used (during playback).
Windows 10 is still a disaster. I've got to install a driver from an older Dell to enable apt-X on my XPS 9350. Codecs and licensing mean that most things will fall back to the lowest common denominator - SBC.
AirPods on Windows 10 is really a disaster, after listening for while, it will go mute randomly (then requires reconnecting), and sometimes sound doesn't match to the other side of pair, few milliseconds apart - which will again require reconnecting. Hence I had to stop using it.
