is there is a way to unbind a skeleton then add or edit a bone then bind it again after recalculating the weight of course
same as animation apps like blender you can create bones then you can bind to see results if you are not satisfied you can unbind and edit
The renderer assumes that a skeleton’s structure does not change over time. If you still change the skeleton (e.g. by adding a new bone), the internal bone texture gets out of sync. This texture has a fixed size based on the number of bones and is used to upload bone data to the vertex shader.
However, you can try to call dispose() on the skeleton after your changes. This will delete the bone texture which means the renderer will create a new one.
for some reason it didn’t work any other idea even if it require editing some source code
const skeleton = new THREE.Skeleton(bones);
const rootBone = skeleton.bones[0];
Mesh.add(rootBone);
Mesh.bind(skeleton);
const hand3 = new THREE.Bone();
skeleton.bones[3].add(hand3);
hand3.position.y = 200;
skeleton.bones.push(hand3)
skeleton.dispose();