No, it is not true that all objects move at the same speed. The speed of an object depends on its reference frame, but different objects can have different speeds relative to a given reference frame.
In physics, motion is indeed a relative concept, meaning that the motion of an object is described with respect to a particular frame of reference. If you are sitting in a moving car, for example, the objects outside the car may appear to be moving relative to you. However, this does not mean that all objects are moving at the same speed.
The concept of rest is also relative. An object is said to be at rest when its position does not change with respect to a particular reference frame. For example, if you are sitting in a stationary chair, you are at rest relative to the chair. However, both you and the chair are actually in motion relative to the Earth's rotation and its orbit around the Sun.
In reality, objects can have different speeds depending on their velocities relative to a specific frame of reference. The speed of an object is measured by the rate at which it covers distance over time, and this can vary between objects depending on various factors such as their relative velocities, accelerations, and the forces acting upon them.