@koyu2 Oh, thanks for the clarification! I just noticed that the walk animation is not moving any bones at all and thus looked as if no animation at all was playing. I will investigade the cause of the problem.

@koyu Unfortunately the code is not minimal, the Character class which calls AnimationState.SetAnimation includes far too much functionality and seems to also call Rigidbody2D.AddForce if some conditions are met. Also there is an unnecessary SkinChanger component which seems to have nothing to do with the issue. Please note that we can't debug your character controller class.

Please create a minimal project where there is only a single script which sets your root-motion-walk animation without any input interaction. If the issue only arises when you add additional rigidbody interaction from code, add this code as well, but in as few lines as possible and without user input interaction. Please remove anything which can be removed.

@koyu2 Oh, I think now I understand your issue. Do you mean that you apply forces to your Rigidbody2D, but when you have the SkeletonRootMotion component set to target the Rigidbody2D, the forces you apply manually to the rigidbody no longer have any effect?

If so, likely your component is executed too early in the update cycle. FixedUpdate of your component shall be called after SkeletonRootMotion. You can set the script exectution order of your component higher e.g. by adding the line [DefaultExecutionOrder(2)] above your class.

An alternative would be to use skeletonRootMotion.AdditionalRigidbody2DMovement which is provided for such a reason:

/// <summary>Additional translation to add to <c>Rigidbody2D.MovePosition</c>
/// called in FixedUpdate. This can be necessary when multiple scripts call
/// <c>MovePosition</c>, where the last call overwrites the effect of preceding ones.

koyu2 [DefaultExecutionOrder(2)]

[DefaultExecutionOrder(2)] didn't have the desired effect of setting the script execution order to after SkeletonRootMotion because under Project Settings - Script Execution Order you have the script set to execution order -4. This obviously overrides the [DefaultExecutionOrder(2)] then.

koyu2 SkeletonRootMotionにRigidbody2Dを適用した途端、velocity_Yの数値がマイナス方向へ増え続けました。ジャンプするとvelocityに数値を代入しているので上空に飛びますが地面に着地後もvelocity_Yは減り続けています。

Unfortunately Rigidbody2D provides no grounded flag itself. As we can't determine safely whether your Rigidbody2D is grounded, you need to perform the test yourself, and then set applyRigidbody2DGravity accordingly.

You could write the test e.g. as follows:

protected bool isGrounded2D = false;

void OnCollisionStay2D (Collision2D collision) {
	foreach (ContactPoint2D contact in collision.contacts) {
		if (contact.normal.y > 0.5f) { // additionally you could check if the layer of the collision object whether it counts as a ground object, accessing contact.collider.gameObject.layer.
			isGrounded2D = true;
			return;
		}
	}
	isGrounded2D = false;
}

void OnCollisionExit2D (Collision2D collision) {
	isGrounded2D = false;
}

@koyu2 FYI: While it is not a fix for more easily setting persistent velocities, we just fixed an issue with SkeletonRootMotion not updating it's references after changing SkeletonDataAsset and calling skeletonAnimation.Initialize(true). See this posting for details:
https://esotericsoftware.com/forum/d/26488-游戏运行中是否可以切换skeletondataasset/3

We will let you know once we have an improvement to offer for setting velocities.

koyu2 最初の投稿の２番目の疑問なのですが、
rootmotionの移動量をボーンのローカル座標ではなく、ワールド座標を参照する方法はないものでしょうか？
もし現在その方法がなければ、将来的にワールド座標でrootmotionの移動ができるようになってほしいと思っています。

Sorry, the RootMotion components sample the animation timelines and support only local-space rootmotion. In general it should not be necessary to support skeleton-space root motion (and it would potentially create problems due to feedback effects). Do you have a setup where the parent of the root-motion bone is moving or scaling? If so, why?

koyu2 理由としては、異なる体型の移動量の違いを表現できず、下記の動画のように別の体型のキャラクターが瞬間移動してしまうからです
The reason is that it is not possible to express the difference in the amount of movement between different body types, and characters with different body types will move instantaneously, as shown in the video below.

Unfortunately I don't understand the problem from your video. What does your bone hierarchy setup look like that that's a problem? Please always share some screenshots of the setup of your skeleton or components if things go wrong, not just a video of the undesired result. Note that we have no idea how your two characters are setup, what is common and where they differ.

@koyu2 Unfortunately me tests have concluded the rigidbody2D.MovePosition can't reliably be replaced by setting (or adding) rigidbody2D.velocity.

A longer explanation:
MovePosition seems to be the only precise and reliable way to set movement delta, for both 2D and 3D rigidbodies. Setting velocity like "rigidBody2D.velocity = movement/deltaTime" works perfectly in mid-air
without gravity and ground collision, unfortunately when on the ground, friction causes severe slowdown. Using a zero-friction PhysicsMaterial leads to sliding endlessly along the ground as soon as forces are applied. Additionally, there is no rigidBody2D.isGrounded, requiring our own checks.

So the best workaround to apply your own forces and velocities is to write your own scripts where you can add forces, set velocities, apply your own drag, etc. Then each frame you can calculate the resulting movement for this frame and assign the value at rootMotion.AdditionalRigidbody2DMovement = movementThisFrame.

@koyu2 Thanks for the detailed writeup. Sorry, my previous answer was actually not entirely correct regarding skeleton space vs local space root motion: Parent bone scale is supported, as it looks like you're using in your skeleton setup. What is not supported is rotation in the parent bones combined with scale and the like. If a simply scaled parent bone breaks root-motion, there might be a bug in the spine-unity runtime.

I just noticed that your description already contains the likely source of the problem:

The "bodysize_all" bone is scaled down by the constraint assigned to the skin

Currently only transform constraints are respected and applied if they are targeting the root bone, but not constraints scaling parents of the root-motion bone.
This is a valid scenario, so we would like to fix this issue. Could you please send us the problematic skeleton assets which has a scaled parent above the root motion bone? Alterantively you could also send us a minimal Unity project again with this skeleton asset.