Feature: allow file transfer between main user and Private Space and vice versa
This can maybe be achieved by Files app. It can use Sharesheet to receive files from apps in the same profile or in another profile, and store them to the filesystem.
It's supported already to an extent.
Currently, the "Save to" option is missing in the GrapheneOS Files app. However, if you use Solid Explorer, the feature is implemented and works well and shows up in the sharesheet
I think this app is currently the best and minimal way to do this
https://github.com/MateusRodCosta/Share2Storage
This would be great to have for the Files app, so you don't need a 3rd party app for it.