How can I use file transfer mode (MTP) once it is connected to a PC?

Hi,

If any USB device is not being recognized by the phone or the phone is not recognized by a PC then most probably there is a problem with the USB port or it's’ connection to the systemboard perhaps.

Use a strong light and a magnifying glass to visually inspect the phone’s USB port enclosure for any dust or debris that may be preventing a good connection on the data pins (pins 2 & 3)

Also ensure that all the pins are there (5) and that they are straight and parallel with each other.

If there is anything lodged in the port enclosure, use a vacuum cleaner to try and get it out. Do not use a metal pin or probe as this may damage the pins or cause an electrical problem in the phone. If it won’t dislodge try using a wooden toothpick to gently pry it out.

If it all appears to be OK then the phone will have to be opened and inspected as to the cause of the problem.

Here’s a link to the ifixit LG G7 ThinQ guide which may help with this.