From within "Graph Editor" you can insert keyframes by pressing the "I" key or by selecting from the "Key" menu. Either way the resulting choices are on a menu that looks broken. There are four items but they are in two offset columns.
This is because the enum prop_graphkeys_insertkey_types has a blank entry in the middle of it. Perhaps this was added to make a separator in the menu, but it breaks it instead. No need for it AFAICT.
The following image illustrates how this looks now on the left, and after the patch on the right: