I don't buy that argument. What kind of keyboard? QWERTY or something else? What language? English is the language of aviation, but if you're not a native speaker who uses keyboards all the time then chances are you're going to have a LOT of mental load using a keyboard. Even something like the French or German keyboards, which use mostly the same letters, may be different enough to cause frustration -- and when you have an engine on fire you don't need to be struggling with those details.
https://www.simpits.org/articles/Boeing_simtour/simtour30.jp...
And English because anything you'd need to enter, like waypoints or airport IDs use roman/latin letters or numbers.
The keyboard is mainly used for planning ahead where you have more data to input. Both are equipped with mouse as well.
You could argue that an onscreen keyboard is significantly less mental load for the pilot than having to scroll letter by letter on a "dumb" interface.
Where do accidents happen? It's fairly rare for a plane to just break. And even then, if your electronics fail there are usually mechanical backups for the critical instruments. It's much more common for pilots to reach task saturation and make mistakes.