@marconirivello did you try it within :devtools? it won't apply anywhere else. I don't know what "Unknown error" is so I don't have any guesses what it could be

Do unused node_modules dependencies get removed from a :target :browser shadow build?

define "unused". if you don't require it then it will not be included in the first place, so no need to remove it. just the presence in node_modules does not mean it is included in the build.