I've configured my Plasma to have this button, it's awesome, and it works for text input in the iced-powered IRC app halloy (I've installed it from flathub).
So far, I have not found many convergent apps written in iced, and, it's still considered experimental and lacks features like RTL support and Accessibility. Soo.. no idea, but no matter what, if you create an app or come across apps by others that work on mobile, let LinuxPhoneApps.org (npub1l3w…lr39) know ;-)