@bbezard It makes sens in older Blender versions (see my following post) to use a separate mesh in order to create a “Shapekey” from a “Bone Deformed Mesh” since “New Shape from Mix” creates a “Shapekey” only from the deformations caused by all currently visible “Shapekeys” together and doesn’t take deformations into account which are caused by “Deformations Bones”. “Shapekey Deformations” using only one mesh are created exclusively in “Edit Mode” whereas “Bone Deformed Meshes” are created in “Pose Mode”. “Join as Shapes” on the other hand can create “Shapekeys” from mesh deformations caused by “Deformation Bones” but it needs a separate mesh.
In other words: „Shapekey“ creations using just one single mesh are only possible in „Edit Mode“ and are therefore excluding deformations by „Deformation Bones“ done exclusively in „Pose Mode“.