Select the Armature first, then the Mesh.
Enter Weight Paint Mode (Armature automatically switches to Pose Mode).
Select the bones to be split in the armature.
Set the "Split Count" in the Bone Split panel (defines how many segments to split).
Click "Split Bone & Weights."
⚠️ Note: Operation in Pose/Edit mode may be unstable in Blender versions below 4.0. Blender 4.0 or later is recommended.
Enter Edit or Pose Mode and select bones to be split.
Set the "Split Count" in the Bone Split panel.
Click "Split Bone & Weights."
Select a mesh object that has an armature modifier.
In the Bone Split panel, select the corresponding vertex group.
Execute the split operation.