I personally learned the MERN stack from youtube.
And here are some of the videos I would recommend 👇
Codedamn MERN tutorial
youtube.com/watch
Pedro Tech MERN Tutorial
youtube.com/watch
JS Mastery MERN Tutorial (Optional)
youtube.com/watch
Any of the first 2 videos is enough to learn.
I would recommend not to waste time watching long tutorial videos, better watch small videos and learn by doing things.