The solution turned out to be . The PC had both Google USB Driver and a generic “MTP driver” assigned to the bootloader interface. Uninstalling the conflicting driver and manually forcing the “Android Bootloader Interface” driver fixed the issue immediately.
fastboot oem help
force flash partitions or use random "unlocker" tools from YouTube—they are often malware. fastboot flashing unlock failed -remote unknown command-
OnePlus uses fastboot oem unlock . However, on newer devices (OnePlus 9/10/11 series), you may see unknown command if the bootloader is already in "locked" state and you use fastboot flashing unlock . The solution turned out to be
You might need sudo for fastboot commands if udev rules are not set. However, running fastboot as root changes the environment slightly. Some bootloaders misbehave when fastboot runs with elevated privileges. on newer devices (OnePlus 9/10/11 series)