cobracommandder7
I understand correctly that you have successfully completed the GrapheneOS installation and now want to transfer files to the device via USB, right?
By the way, the developer options are not required for file transfer.
Have you checked the following settings?
Settings> Security> USB peripherals
and Settings> Security> USB-C port
?
Depending on the settings - when you connect a USB cable, a pop-up window usually shows up saying something like "charging device. Tap for more options." If you tap it, you should be offered several options, including "File transfer".