It is a letter ring, not a keyboard
There is no typing here. Every level gives you a small ring of letters, and the whole game is swiping across them in the right order to spell a word that belongs somewhere in the grid above. Get it right and it locks in; get it wrong and nothing happens except that you try again.
The letters in the ring do not change between words within a level - the same handful gets reused for every answer, which is what makes the puzzle work. A four-letter word and a six-letter word from the same level are drawn from an overlapping pool, so solving one often makes the next one more obvious, because you have effectively ruled a few letters back into play.
The shuffle button exists because a ring can sit in an order that is genuinely awkward to trace with a finger, particularly on a phone. It does not change the puzzle - it only rearranges the letters in place - so there is no reason not to use it whenever the layout feels clumsy.