my Camry V6 2007 is on parking, and not engaging any gear (( could it be somewhat related to the fact that the front breaks are very, very worn ??? - no problems with the gears before that..

If you are saying it's stuck in park, there should be a tiny access panel just to the upper left of your shifter. It's about the size of a postage stamp. Pry it open. Stick a pen or screw driver in the hole and push down the button. You should now be able to get your car out of park. It's not your brakes that would cause this. Usually a bad solenoid in the shifter. Here is a short video: https://www.youtube.com/watch? v=FhXeGKypsQ0