I will add that it MAY make a difference if you are using SquareSpace 7.0 or 7.1. This really screwed me a few months ago on other features and I had to remodel my entire site to work in a new 7.1 template. SquareSpace upgrading everything around February and if you are on 7.0 still, which many are, some things work differently. Just something to note and that’s definitely not a Twitch issue. Beyond that Javascript should work in the Embed module and the iFrame should work in both the video and Embed Modules. You could inject the code too but I know how much of a pain that is.