In the forum, I saw a couple of people suggesting,
- Syncthing (But Syncthing for Android is dead, AFAIK)
- USB stick
- Cloud storage
Please suggest if there are any alternatives. Or what is the option that you’re using.
- Anything where you put the file somewhere under profile A then read it under profile B will work. - Depending on why you want to transfer a file between profiles there are probably different tools you’ll like. 
- Thanks for link 
- Does it work over always on VPN? - Yes 
- Sorry I’ve never actually tried it, I just knew it existed 
 
 
- There is a syncthing fork that is being maintained. - Oddly enough, it’s called Syncthing-fork. - https://github.com/Catfriend1/syncthing-android - Last build is 15 days old. - Hah well how about that. 
 
 
- If files were easily accessible between profiles, wouldn’t that harm the privacy of having multiple profiles? - Not necessarily. It would provide an attack vectore for sure, that being the data connection between profiles, but if it is implemented in a controllable manner (See qubes os), it’s fine. The only issue I see with GrapheneOS in this scenario is: There is no uncompromised host for verification, so I don’t really know myself how something safe could be implemented, however I would also think devs don’t really want to, since there are ways which OP has already described some of. 
 



