Dumb question but I'm new to itch.io - how do I upload a webgl build as well as a download version? I've seen some people have them on their submissions last year.

When you have more than one file, you can choose one as your file to be played in the browser and one as a downloadable executable file.

It is indeed a bit confusing. At least (thankfully) the project type can be changed to be a browser playable game later.