With the app you can also change the cancellation level, they’re pretty isolated even with the feature powered off entirely but it helps out in some situations.
My Boses allow you to set the cancellation level with a button press. It cycles through three options: high, low, and off. Does the app enable more fine-grained control or something? Perhaps per-ear cancellation settings?
Apparently so. I have the QC35 II, which has a button on the left ear can. Bose calls it the Action Button, and it's used to summon Alexa/Google Assistant; but if you don't configure it to use an assistant (through the Connect app?) it will cycle through the noise cancellation level settings.