Using the current default animation editor, it is currently too hard to add a keyframe at the slider like in the previous default animation editor. Currently, users need to press the ..., then press Add Keyframe button. Previously, users could press the K button to add a keyframe to all the selected limbs.
Example of Adding Keyframes on Current Editor
It is currently much slower to add keyframes than on the older animation editor because users must open a menu to press the button and can only work with one limb at a time. Please add the K keybind back.