OnePlus
Change USB Connection Type auf OnePlus
By default, a OnePlus phone treats a USB cable connected to a PC or laptop as a power source only. This protects your data from being accessed automatically, but it also means file transfer, PTP (photo transfer), or MIDI mode will not work until you switch the mode manually.
This setting lives in the connectivity section of the system settings and only appears once a USB cable is actually connected. If you open it without a live connection, some options may be missing or greyed out.
Where to change it
Open Settings ➔ Bluetooth & device connection ➔ USB ➔ choose the desired USB preference. You will typically see options such as file transfer, photo transfer (PTP), MIDI, or charging only.
Pick file transfer if you want to browse, copy, or move files between the phone and computer. Pick PTP if a camera or photo app expects a photo transfer protocol instead. Charging only stays the safe default when you just want to power the device without exposing storage.
If the USB menu does not appear at all, check the cable first. Some charging-only cables lack the data lines needed for the phone to even offer these options.