access to filesystem

[syddo]

is it possible to access the filesystem from the Rust side?
ie. write to file or read to file.
in my understanding from initial reading of the Documentation, this is possible. actually in the development environment I am able to write files to the file system (tested this on macOS BigSur as of this writing). the problem is that when the application is bundled, it is no longer able to write files.
is there something i'm missing?