Track View menu bar > Keys > Use Soft Select
Track View menu bar > Utilities > Track View Utilities > Soft Selection Settings Manager
Displays a dialog with controls to adjust the range and falloff of the soft selection of keys in the Dope Sheet and Curve
Editor.
Soft—Toggles usage of the soft selection. When this is off, only the selected keys are used, the soft selection is not.
Range—Determines the range of keys affected by the soft selection.
Falloff—Determines the distribution of the strength of the soft selection over the range of keys.
