I gotta say, as far as online videos go, there's nothing that stands out to be an immediate recommendation.
And it's hard to sift through all the crap to find the gold. But there's always new stuff coming out. Have you googled or searched youtube at all?
Shiu (and almost all professional animators) will recommend you Animator's Survival Kit. It's a book. There's also a tie-in video series by the same title.
The book itself is great. Don't be fooled by its outdated style and medium. The important thing it teaches is what to look out for and how to analyze movements, as well as what techniques have been tried and tested (and are still applied to this day). Without that framework, you can stare at animations all day and all you'll ever get are vague feelings of "that doesn't feel right" or "that's really cool" and you won't know what to change to make movements better.
The rest of the work of "becoming a better animator" is just looking at animation you love. Staring at it. Analyzing it. Copying it (or at least trying). Improving on it. Mixing from different inspirations. And of course, practice practice practice. Your taste (your ability to tell what's good and what's bad) will always develop faster than your skill (your ability to actually achieve what you think is good) and practice is what'll make your skill move forward.
And just as a personal opinion, most "3D Animation" tutorials aren't good animation tutorials.
3D programs and systems are super technical. Modeling is very involved. Rigging and texturing isn't intuitive. Most tutorials end up being too much about the program and barely about the art of animation itself.
So if you're going to bet you're time or money on tutorials that teach you animation, go for the people who do hand-drawn animation. Their techniques are applicable in 3D and in Spine and in motion graphics and whatever.
