It is always fun to see how Sudoku solving algorithms are created and implemented. This is no exception: [WayBack] Coming Back to Old Problems: How I Finally Wrote a Sudoku Solving Algorithm - DEV Community 👩‍💻👨‍💻

(backtracking image from Wikimedia commons)

For a visual Sudoku solver, I usually take [WayBack] Sudoku Solver by Andrew Stuart. Shows the logic behind solving Sudoku square by square which is part of [WayBack] SudokuWiki.org - Getting Started having many visual explanations on how to solve these puzzles, for instance:

It's a kind of sudo ku, but visually and never failed me solve one.

--jeroen