This app was mentioned in 6 comments, with an average of 2.33 upvotes
I know its not ridiculous fishing or bloons, but I've had this for years across many, many phones, and I still love Sudoku.
I used to play using this app here, I managed to find it again pretty fast: https://play.google.com/store/apps/details?id=com.icenta.sudoku.ui
It really is just sudoku, it's good, only banner ads on top.
On android there is one called Sudoku by genina.com which has an option in the menu to autofill pencil markings.
I think there are a bunch of free Sudoku apps.
Something like this https://play.google.com/store/apps/details?id=com.icenta.sudoku.ui&hl=en