Check out Why does fs.writeFile not save file? - #2 by joethei where joethei talks about how fs is not present on mobile platforms. So part of your issue is to be expected, although not documented on the Obsidian documentation site.
Not sure if something or what has happened to the path functions, but if we’re using parts of the API not documented, I’m thinking that’s a risk we’re taking. If it’s documented though, then deviations from the API could be considered a bug (or possibly unannounced change to the API).