What's wrong with this version? Сучасні планшетки можуть все робити.
I guess планшетка was decided to be too colloquial * shrug *
But I say exactly this word for the tablet. To be планшет (without ка) is a different device, the one for artists to draw using a kind of pen instead of a mouse.
Exactly: everyone I know in Ukraine says планшетка, mainly because they are usually small Yet when the sample sentence was about rivers, Duolingo accepted річка but not ріка, although we never say річка Дніпро!