I noticed in an older topic that talked about Brotli support for Unity WebGL games. https://itch.io/post/1987680. When I tried it today it didn't work for me yet. I assume Brotli is not supported yet by itch. I noticed with my smaller project, the size difference was about 2mb (total 8mb Brotli vs 10mb gzip). I will use gzip for now.