Camera is not working on Web
Version 3.0.2 of mobile_scanner uses a different qr decode library. It is loaded from an CDN. The issue is, that it tries access the library before it is loaded. So a JavaScript Exception is thrown and the execution of the code will be stopped. There are two open closed issues on Github ragarding this problem (#622 and #637). This comment suggests a possible fix.
Note for my self: Remove the old one, add the new one, keep care that it blocks the process on loading and that the service worker saves it locally.
Maybe i should simply change the source of the plugin from https://pub.dev to the Github repo. Seems to be solved there.