I’ve beed asked from Steinberg a few days ago about a bug I reported since N13. Select multiple tracks from an external DAW controller is broken. It ran well until N12. I think after several service tickets Steinberg is working now on it and I hope the repair of this issue helps also the wrong function you talk about.
It’s a matter of when you press the modifier keys, unfortunately.
You have to press Alt + Shift before you click on the Input or Output field of one of the channels. After the click you can release the keys and select a new input or output.
Previously, I have used this feature by clicking on it, once the menu was showing, and while I tried your way and it worked, being on a larger monitor now, I am wondering why there is all of this click-thru, with shortened menus, and folders, as well as the incessant need to drag scrollbars, which just makes the job laborious.
Cheers, and thank you for saving me loads of time!