I couldn't figure out why the sensitivity of the mouse is messed up in the WebGL build I received. As you can see in the YouTube video, it actually works fine in the Windows build.
The reason the enemies are flying might be due to the animations I got from the Mixamo website. When animations are not custom-made for the characters, you can encounter such movement issues, unfortunately. Since I have no knowledge in modeling, I couldn't resolve this issue.
In theory, anything with the "ground" tag should be jumpable, and I will check on that. Thank you for your feedback and insights.