For game art in general, Riot games released a series of videos on their Youtube channel that explain the different areas.
And for animation, we think every animator would agree that "the animator's survival kit" is THE BOOK. As it explains the basics that pretty much every animation follow.
Now, specifically for games, we are big fans of the YT channel "New Frame Plus". Dan really loves animation, and you can notice from his videos, he explains in detail every aspect of the animations and why they do or don't work well.
Also, https://80.lv/ and https://polycount.com/ very good sources of information and feedback regarding everything in the world of art for games.