This is a project that happened to obsess the contributors on a greek island in the summer of 2022: figure out how to generate and solve sudoku boards of arbitrary size, without looking at any existing theory of sudoku. Obviously, the kind of vacation that inspires one to reinvent the wheel.
If you're a PHP person you'll probably know how to get the whole thing up and running. If you're like the person writing this README, you'd be well advised to make sure you have a PHP version of at least 8 installed, just to be sure that you have all the current goodies, then clone the repository. Visual Studio Code, with a couple of appropriate PHP plug-ins, is not a bad choice of IDE if you feel like fooling around with the code but you don't have access to fancy things like PhpStorm or similar.
You can then run PHP's built-in server by
...:~yasu$ php -S 127.0.0.1:8000
and load the frontend on http://127.0.0.1:8000/ on your browser of choice, to actually play. There's no need to bother with heavy-duty tools like XAMPP -- which, in the experience of the contributors, isn't even guaranteed to work out of the box in such systems as Ubuntu 18.04...
Let's all hope that this README gets updated soon by a more knowledgeable person -- till then, have fun, with or without sudokus!...