I recently updated Revit LT to the newest version (2021) and encountered a problem with the software.
When I went to load a family into my project, there are no libraries whatsoever! At first, I thought I missed something during the installation process but after a little research online, I found out that Autodesk by default does not include the libraries anymore in the installation anymore (I have a feeling that they will be doing that from now on)
They added a button on the Insert tab "Get Autodesk Content" that when you click will take you to the download page for Revit families based on Country (U.S., Canada) and Units (Imperial, Metric)
Most likely, you would want to download "Imperial Libraries"
It will download a packaged software that will add the libraries to your Revit installation - Make sure to have Revit closed before running the install file.
Once its installed, open Revit and head to Load Family and it should directly open the families folder! I hope this helps!