CryptoMares CharacterBody is KINEMATIC, it is not moved by physics, it is moved by code.
if you want the player to react to physics you need to use a rigidbody.

if you want to measure the speed of a CharacterBody, the best way is to store the global_position in a variable and compare it with the global_position:

var last_pos : Vector3
var curr_speed : float = 0.0

func _ready():
     last_pos = global_position

func _physics_process(delta):
     curr_speed = last_pos.distance_to(global_position)
     last_pos = global_position

I believe you can divide curr_speed by delta to get the speed per second:
curr_speed = last_pos.distance_to(global_position) / delta

      Jesusemora Is there any way to add this kind of behavior to a Kinematic body? Rigid body will introduce a bunch of unwanted behaviours, that will need to be mitigated, I believe. Am I wrong?

        Megalomaniak I would love to learn how to use tweens for stuff like this. I would like to tween most of my variables, I don't know how though, I'm a newbie.

          kuligs2 Well, lerp is linear and I would like a curve. Ideally, a custom curve that I can control precisely.

            You could try to do something physics-like: measure your velocity, and then if no input and touching the ground: change it progressively to zero. If not touching the ground: change it progressively to straight down.

              axolotl That's too advanced for me to figure out on my own right now, unfortunately 🙂

                I've been working on an answer for a few days. This has been something I've wanted and tried to do for a while now, so I'm happy that my asset was just accepted to the AssetLib! It's called Rigid Character Body 3D, if you're using Godot 4.2 or later you can take a look at it. It's not the greatest thing ever but I think it does a good enough job to get you going on this.
                It extends RigidBody3D and adds movement forces and drag which creates a simple and configurable character controller.

                  wabbit why? 😃 GPL means that if you use it in your project, the rest of your project has to be published under gpl aswell.. and other stuff.. idk.. but ok 😃

                    wabbit That's awesome, thank you! However it's not exactly what I'm would like to achieve, I would like something of an imitation of momentum added specifically to a Kinematic Character Controller.