I made a custom ride using the macOS client, under the assumption it was going to be available to me in the iOS client. It wasn’t. I think any custom rides you make should be available in every client, on every platform. Not tied to the device you made them on.
custom workouts save locally to the machine you made them on because there’s no cloud storage for them, much in the way if you take a picture with your phone you’ll need to use some kind of cloud storage (native to the phone or otherwise) to access it on your computer.
you could always email the custom workout to yourself and then download it and put it in your workouts folder on whatever device you want to use.
or you could make the custom workout on trainingpeaks or some other 3rd party site and have that linked up with your account, those will show up on whatever you log into zwift with
T boi is correct, as even though they are iOS devices, they are entirely separate from one another. But an automatic sync from device to device just based on logging in is a cool idea! Thanks for letting us know how you feel :)