Hate to be that guy, but I copy paste clipboard contents across devices with kde connect. It's so reliable that I tried doing it when fixing my mum's computer without realizing it's not a magic built in thing that computers just do for some reason.
That's because it's impossible to implement that functionality in iOS with its locked-down APIs. It's the same reason that Microsoft's Your Phone app is limited on iOS compared to Android. On iOS, only Apple has the privilege to implement such features and they limit the interoperability with macOS.
Considering that your're not allowed to do anything interesting with the system when developing for ios, that's not surprising to me. I connect my android with my gnu/linux machine and my windows videogame box, that's all I tested.
