Unity2D - natural physics for two colliding spheres/balls - unity3d

Question

In my 2D Unity game, balls can bounce off each other. My goal is to have them bounce off each other as you would expect physically in the real world.
The only difference is that the speed of the balls decreases, but they can never come to a stop.
I have different approaches to map the physical behavior. But none of them leads to a good result.
(1)
private void OnCollisionEnter2D(Collision2D collision) {
var point = collision.GetContact(0);
var curDire = transform.TransformDirection(Vector2.up);
var newDir = Vector2.Reflect(curDire, point.normal);
transform.rotation = Quaternion.FromToRotation(Vector2.up, newDir);
speed *= 0.75f;
}
I don't know how describe exactly: It can happen that the balls push past each other. They collide, but do not bounce off each other, but maintain their direction.
Another approach I have read about is to add an AddForce to the velocity of Rigidbody2D.
Then the following code should do the physics.
private void Start()
{
rb = GetComponent<Rigidbody2D>();
_velocity = new Vector3(1f, 1f, 0f);
_rb.AddForce(_velocity, ForceMode2D.Force);
}
private void OnCollisionEnter2D(Collision2D collision) {
var inDirection = GetComponent<Rigidbody2D>().velocity;
var inNormal = collision.contacts[0].point;
var newVelocity = Vector2.Reflect(inDirection, inNormal);
rb.velocity = newVelocity;
}
The results are really random. I think I use a wrong AddForce or the velocity-Vector is strange. I fall here the deeper mathematical understanding to fully comprehend this solution.
(3) Then I read about Physic Material 2D. This sounds best. I created one (Asset -> Create -> 2D -> Physic Material 2D). Set bounciness to 1 the friction to 0.1. I select my Ball-prefab and add the physic material to my collider. I added it to the Rigidbody2D, too. But this asset has no effect. (My balls have no gravity. I don't know if this is important.)
I imagine Unity has a super simple solution for this problem. But I just can't find it. Does anyone have any ideas or approaches for me? I actually just want shot balls to bounce off each other. This should look as much as possible like it would look in real life.
Update Question
I move the ball like that
private Vector3 _inDirection;
private void Start()
{
_inDirection = Vector3.right * (speed * Time.deltaTime * (_didCollide ? -1 : 1));
}
private void FixedUpdate()
{
transform.Translate(_inDirection);
}