My old post here had code that worked at one time that did real native file system operations on IOS and Android using a Cordova module that has since changed. If you want non-browser non-prompt file system access it should be as simple as finding a Cordova module without broken npm-fetch and using it..
A lot of stuff on npmjs->"keywords:ecosystem:cordova" breaks under SB now. I never checked why but you have to find a FS plugin that doesn't and use their demos or documentation to get what you want. It's the same with the old Camera and WIFI AP code I posted here too I think; it all worked at one point, but SB won't import certain npm-cordova stuff based on some internal filter or repo-domain.
FYI "cordova plugin add cordova-plugin-file" is W3C browser API and requires MAC to use; it's what SB uses. Other file modules will likely break on import..