Seen a lot of people confused on how to host WebGL Unity apps on Neocities - figured I would offer some help! Here is a solution I have found that works.
First, follow this guide.

Then, create a iframe in your pages html that links to the repo you hosted on github.

<iframe src="https://[YOUR USERNAME][YOUR REPO NAME]/" style="border:0px #000000 none;" name="Game name" scrolling="no" frameborder="1" marginheight="20px" marginwidth="px" height=850 width=100% position=absolute></iframe>

Width and height can be adjusted to your specifications. Pretty sure there is a way to host the file locally on your page itself if you are a supporter, but I haven't found a way to do that directly yet. Hope this helps!