In case you didn’t know, you can install a different onscreen keyboard from Discovery. It’d be nice if the default keyboard didn’t lack those fundamental features, though.
Not with the one I installed (CoreKeyboard). And it’s only usable in Desktop mode.
Once in Desktop mode, you have to launch it (or set it to auto launch). Then it puts an icon in the system tray and you can click that to show the keyboard. There’s a key on the keyboard to hide it.
There’s probably a better keyboard out there for the Steam Deck specifically, but for my purposes it works well enough.
I use barrier when I need a keyboard in desktop mode. It works well. I just need to remember to turn off the server afterwards, or my desktop can't fold !