I thought I could share the resources I used to reduce the size of my Unity build, since I'm trying to get my game running in Firefox, on a potato.

A tool to optimize your project within Unity (small hint, your textures fault): 

https://docs.crazygames.com/other/unity-optimizer/

A blog with a few articles about optimization for Unity: 

https://www.techarthub.com/category/unity/

And finally if you use a compression method for your build (Brotli here), you might get an error on itch.io, so be sure to check that option so your game embarks a small tool to do the job!

Project Settings > Player > Publishing Settings (WebGL Tab) > Decompression Fallback

Good luck!!!