Something that has really ramped up my ability to calculate quickly is a game called “unBlock Me” on the Android.
There are bunches of games like that, just type “unblock” when searching for an app. I’ll presume the same games are on the iPhone. I used to play one using different length cars, but my old phone died on me, and when I went to get that type of game again, the one I’m using popped up first. Both are essentially the same thing though.
You move different length blocks or cars around to get the highlighted block or car (or some other graphic, but most seem to be cars or wooden blocks), through a doorway and off the screen.
Just type “Unblock” in the app store.
I’m at the expert level on my current game, and it really helps to hone your cognitive thinking skills.
I’m sure there are plenty of other games out there that help you hone your cognitive skills. Feel free to post your favorite on this thread.