It works like it always has/ is designed to work. AE never selects anything based on a search field. Not in the project window, not the timeline, not the E&P panel. Kinda makes sense most of the tiem, considering how much actualyl depnds on the selection context in AE...
I just to make sure I'm not getting an answer from miscommunication. Ie. I search up motion blur in the effects panel... I'm not expecting to hit enter in the search field and then it being applied to the layer... I'm asking if I can some how "tab"/jump down to the results list and arrow key through that and then hit enter on the effect i want....Hopefully that makes sense....
Cmnd/Ctrl + 5 will get you to the Effects & Presets Panel or open it if it's not visible (or hide it). Unfortunately you cannot use the Tab or any other keys to jump to the query field or navigate through the presets.
Shortcuts to all of the panels that have shortcuts are right there in the Window Menu. It's a good way to learn shortcuts.