I have a game called Wordsmyth, I paid some trivial amount for it, it’s basically a 3x3 grid of nine letters and you make as many words as you can out of those letters. Very basic concept. Incredibly addicting. Those last words are quite difficult to find. I very rarely get them all in one day. Fortunately you can star a game and keep it for later.
Attractive, simple interface, zero ads or annoying pop-ups. It doesn’t even have any intrusive features. Everything about it appears designed to give your brain a break.
The only real downside is it’s a bit of a battery drain. The developer is working on it.