How is the action in intellij called to show the line-diff overlay?

I often utilize the intellij functionality to show the diff for some lines in the in-editor overlay, which can be found in the gutter as a blue (or gray, green, depending on whether the change is a modification, addition or deletion) bar:

I wonder if it is possible to assign a keyboard shortcut to this feature, i.e., what is the name of this action (under which it could be found in the keymap settings) ?

You are looking for the action Change Under Caret, which you can find at Version Control Systems > Change Under Caret in the keymap.