There are some good options for transferring files between user profiles.
I personally can recommend the following:
Syncthing
Has already been mentioned here; I find this post for setting it up quite helpful:
https://discuss.grapheneos.org/d/6950-how-do-i-sharetransfer-things-across-profiles-on-graphene-os/6
Transfer via USB stick
Drag files in profile A to an USB stick, change profile and copy files from the stick to profile B.
if you feel uncomfortable having the files unencrypted on a USB stick, you could, for example, encrypt them with Cryptomator in profile A and then copy them to the stick. Then copy them to profile B and decrypt them there with Cryptomator as well.
Transfer via cloud
Here you can either install the app (e.g. Tuta, Proton) in both profiles and move the files back and forth via the cloud. If you only want to copy files in one direction (e.g. always from the owner profile to the user profile), it would also be sufficient to install the app in only one profile. From this profile, you give the other profile access to the data via a (password-protected) download link.