If the pendulum is released with zero speed, it can never rise above the initial point of release since that would imply free energy.
As the pendulum moves through the air, friction from the air molecules resist its movement. This changes some of the pendulum’s kinetic energy into thermal energy, which is transferred to the environment. With less kinetic energy, the pendulum slows down. When all of its mechanical energy has been converted to thermal energy, the pendulum stops. It no longer has potential energy or kinetic energy. But the total energy in the system remains the same.
