Formula for acceleration to reach max velocity

Hi!

I tried to get a formula for calculating max velocity of a rigidbody, but after couple of days of trial and error, where I tried to apply some physics formulas to find my values I got nothing because I was unable to figure out how unity calculates all of this.

I got some results from this formula found on the forums(without gravity and friction):

 maxVelocity = ((force.magnitude / drag ) - fixedDeltaTime * force.magnitude )/ mass;

and force is just:

 Vector3.forward * mass * acceleration;

Right now I need to set the acceleration to achieve max speed, but can't quite get the formula right for this. Is it even possible? I have tried transforming this formula, but I failed :/ (the shame!)

This is for a rigidbody without gravity and any friction.

some code:

 public Rigidbody r;
 public float acceleration = 1f;
 public float currentForwardSpeed ;
 private Transform _t;
 private float force;
 
 void Start()
 {
   _t = GetComponent<Transform>();
   acceleration = ???????
   force = _t.forward * r.mass * acceleration;
 }
 
 void FixedUpdate)
 {
   currentForwardSpeed = _transform.InverseTransformDirection(_rigidbody.velocity).z;
   if(Input.GetKey(KeyCode.W))
   {
     float maxVelocity = ((force.magnitude / r.drag ) - fixedDeltaTime * force.magnitude )/ r.mass;
   }
 }