It is a poor security practice to
  store secrets in an app.

Supported targets

The following build targets
support the obfuscation process 
described on this page:

aar

apk

appbundle

ios

ios-framework

ipa

linux

macos

macos-framework

windows

Web apps don’t support obfuscation.
  A web app can be minified, which provides a similar result.
  When you build a release version of a Flutter web app,
  the web compiler minifies the app. To learn more,
  see Build and release a web app.

Obfuscating your app