i want a rigidbody cube 3d to stay at a constant speed

all the other answers i have found all say Rigidbody.velocity dosent exisit someone help please. an example is this

Rigidbody.velocity = new Vector3(100, 0, 0) * Time.deltaTime;

everything is fine except Rigidbody.velocity

Are you using a particular reference to an instance of a Rigidbody? You can’t access Rigidbody.velocity statically, you have to do something like setup a member variable like this:

public Rigidbody rigidbody;

You can assign that by code or in the inspector, and then you can access that instance’s (“rigidbody”) velocity field.

You need to assign your rigidbody first.
Before Start() write: Public Rigidbody RB;
Then in Start() write: RB = GetComponent();
And then in Update() write: RB.velocity = new Vector3(100, 0, 0) * Time.deltaTime;