Some good news potentially @freddydumont - I can’t say I’ve tested it thoroughly or anything, but I think netlify will automatically optimise images for you (its in the post processing section).
Alternatively worth a look into https://github.com/webpack-contrib/image-minimizer-webpack-plugin
Webpack is powerful but can be super annoying. Here’s another thread (for a completely unrelated problem) where I walked through adding to the existing RW webpack config CORS issues when developing locally against a separate API server