The keyboard situation on Wayland and especially KDE is abysmal. Through a workaround I managed to get Onboard working. But it often crashes for me when using it with touch.
The keyboard from Steam actually works best for me. But I don't know how to pull it up without a gamepad. I've got a post showing how to get it working outside of the Steam Deck. https://swg-empire.de/post/853437
All in all I actually think that Gnome is better suited for touch devices. But I just don't like how it works overall. But maybe your girlfriend likes it.