This is a feature called reachability. It's built into iPhones so you can reach stuff with one hand.
You can disable it by going to Settings -> Accessibility -> Touch and toggle Reachability.
Also, if you want to know how to use it, tap the home button twice (some call this gesture a wiggle) without clicking it or swipe down on the home bar.
This is required for the EasyRide functionality. The first time you activate it within the app you are asked to grant access by iOS.
(EasyRide wants to access your Fitness data to optimally support you, e.g. if you forget to sign-off after a trip)
If you decline you can't use the EasyRide functionality
You can check in System Preferences -> Health ...
Go to System Preferences → Bluetooth and for your AirPods choose Options and set ‘Connect to This Mac’ to ‘When Last Connected to This Mac’.
Now your AirPods won't automatically switch away from your iPhone to your Mac. Make the equivalent change on your iPhone to stop the other way round.
Then your AirPods will always connect to the last device and you can ...
I'd say one does not exist.
The reasoning behind you being able to find an adaptor from USB-C to lightning is that both are digital connections. I'm not sure what, if any, data translation would need to be done, but if it was necessary USB-C can carry the power to do it. (Similarly for the lightning to audio cable supplied with the iPhones).
To do the same ...
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