Set up a web server before (you can use httpd) and then copy the files of the game's www directory to your specified root folder (e.g. /var/www/htdocs/game)
$ doas cp -R /path/to/game/www/* /var/www/htdocs/game
Your saves are stored on Local Storage in the browser so you can use this on the web console (usually you can open with F12 and go to the "console" tab) to export:
copy('var data = '+JSON.stringify(localStorage)+';Object.keys(data).forEach(function (k){localStorage.setItem(k, data[k]);});');
Then, paste the new content in a file and to import this only copy the content of your file to the web console and run it, after that reload the page and it's done.
PS: Crosscode (uses nw.js but is not a RPG Maker MV game) can export or import your save as a savestring when you press F10 in the game. This is already documented upstream.