I do historical research in the context of legal work, and for that Hein Online is pretty good. It’ll have old copies of speeches given in Congress, contemporaneous articles, and that sort of thing. It also has tons of old articles and research papers in the social sciences. ProQuest is indispensible for more modern stuff. If you’ve got a Library of Congress card, many of these resources are free.

A lot of stuff just isn’t online. For one case I needed to look through a bunch of 19th-early 20th century rail and telegraph tariffs. These were generally published in booklets, but they were commercial materials so the Library of Congress doesn’t have many examples. But EBay did!

As a millennial I fall into the trap of thinking if it’s not Google it doesn’t exist. But the traditional methods your librarian taught you are still highly relevant even today.