How to NOT include streaming assets in certain builds

When I build my app for any platform, Unity adds whatever is in the streamingassets folder, also when it has nothing to do with the target platform.
So my Android app gets my WebGL and Standlone OSX assetbundles, making it 3x as large for no reason.

Is there a way to tell Unity not to add asset bundles?

 

There is no build in way but you might like to take a look at IPreprocessBuildWithReport

https://docs.unity3d.com/ScriptReference/Build.IPreprocessBuildWithReport.OnPreprocessBuild.html

It should allow you to move any file you do not like to include from your streamingassets folder on a per platform bases out of the streamingassets to a temporary location and use IPostprocessBuildWithReport to move the files back after the build.
https://docs.unity3d.com/ScriptReference/Build.IPostprocessBuildWithReport.OnPostprocessBuild.html

 

Also depending on your circumstances, your deadlines, your willingness of exploration, you can take a look and play with the Scriptable Build Pipeline.
https://docs.unity3d.com/Packages/com.unity.scriptablebuildpipeline@1.5/manual/index.html