Use CircleCollider2D in circular object and BoxCollider2D in rectangular objects.

Use a Physics2D Material in both colliders. Set Friction = 0 and Bounce = 1.

Use force to shoot the projectile. Use Impulseas ForceMode2D.

If the circular object is using gravity then it will lose it's exact path after deflection but depends on amount of force applied.

If the circular object is not using gravity then intended path won't change.

In both case you are getting precise angle after deflection cause of zero friction and full bouncy physics material. But the path depends on gravity.

Use CircleCollider2D in circular object and BoxCollider2D in rectangular objects.

Use a Physics2D Material in both colliders. Set Friction = 0 and Bounce = 1.

Use force to shoot the projectile. Use Impulseas ForceMode2D.

If the circular object is using gravity then it will lose it's exact path after deflection but depends on amount of force applied.

If the circular object is not using gravity then intended path won't change. But this isn't defined as projectile.

In both case you are getting precise angle after deflection cause of zero friction and full bouncy physics material. But the path depends on gravity.