Ingonimania You don't need to change the USB-C port control setting added by GrapheneOS to use USB file transfer, etc. You should set it back to the default of "Charging-only while locked". That only means you can't start new connections while locked. It will connect after unlocking.
macOS doesn't come with support for MTP. You need to install an application providing MTP support. File transfer is off by default with the standard Android approach and needs to be enabled via the USB menu. A notification appears with a shortcut to it when there's a USB connection.