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.
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.
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).
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