Then use minicom or picocom on /dev/ttyUSB0 .
You won't see "MT6261" in Device Manager while the device is idle. The driver only activates when the phone is powered off and connected correctly. mt6261 usb driver
If you still face issues, inspect your device's boot ROM health. A dead battery (below 3.3V) will prevent the MT6261 from entering download mode, even with a perfect driver. Then use minicom or picocom on /dev/ttyUSB0