Power flowing through a cable does not prove that the cable and current connection support file transfer. Work through the cable, phone mode and receiving computer as separate checks.
Check the physical path
Use a cable known to support data, connected directly where practical. Some cables are designed only for charging. Try a different appropriate port or known-good cable without changing several things at once. Avoid forcing a connector that does not fit.
Unlock and choose the intended mode
Unlock the phone and inspect the USB notification. Select the supported file-transfer option when prompted. The exact wording varies across devices. Keep the phone's security requirements in place; a locked-device restriction is not a reason to disable broad protections.
Test one ordinary file
On the computer, use its supported file-management flow and copy a small non-sensitive document. If the phone does not appear, record the operating system and what the USB notification shows. If it appears but a file fails, note the file type, size and destination.
Verify before disconnecting
Open the copied file on the receiving device, close transfer windows and follow any normal eject procedure. Keep the original until the destination copy is verified. If the problem persists, use the device manufacturer's current USB guidance rather than installing an unknown driver utility.