I read on youtube that when you reach 500m if you press the rth button and keep the trottle up then you can go higher. Is it true?

Like a lot of things you might read ..... No.
Don't even think about it - the 500m limit is hardwired

Didn't try it. I wouldn't like to risk my drone, and what is more important i wouldn't like to risk other airplanes with 100+ people on board that could be around going unreasonably high

Imagine your struck into an Airline engine going that high and caused many lives, that Guilt gonna hunt you for the rest of the life, so why going off the limit when you were given 1640ft which can shot amazing and beautiful videos? Im happy DJI implement this restriction to protect this hobby and customers