I noticed that the search of the Library Manager doesn't search for the perfect match, but libraries that contains the text and sort it in a random order. The library you're searching for could end up in the middle instead on top of the list.
For example. Search for WifiNINA in the search of the LM. The WifiNINA library is the 16th item in the list after the alternative libraries. In the Arduino IDE 1.8 it is the first item at the list.