Sharing files requires a bit of creativity.

You can share with file synchronisation apps like Syncthing/Ouisync [0], exploit a temporary weakness in the isolation model with Inter Profile Sharing [1], or simply copy the files over to an external storage device and transfer them that way.

[0]https://github.com/Catfriend1/syncthing-android

[0]https://github.com/equalitie/ouisync

[1]https://github.com/VentralDigital/InterProfileSharing

I've successfully used Material Files [1] to set a nework shared folder (I think it was FTP) on one Android profile, and accessing it ("connecting" to it) from the other. So this might also work between GrapheneOS profiles.

[1]: https://f-droid.org/packages/me.zhanghai.android.files/

See: https://github.com/VentralDigital/InterProfileSharing

It also shows that profiles can't really prevent an app from correlating profiles on the same device, by listening on a local socket.

If you disallow Network permission to an app (a GrapheneOS feature), local network access is also disabled.

You can use Seedvault to make and restore a backup. Set up a secondary user profile with settings only (no apps yet), make a backup and use that in future for initializing other profiles.

There are apps like Inter Profile sharing (appID: digital.ventral.ips).