We currently have a serious production issue with two SharePoint Online customers. On Classic Pages when you add an Angular app, the app does not work. There is an error in the console: Zone already loaded.
On Modern Pages Angular apps still works.
According to this post: https://stackoverflow.com/questions/66469814/sharepoint-online-angular-error-uncaught-error-zone-alr... the workaround is to add the following code.
window.Zone = undefined;
Microsoft is pushing the following file which contains a lot of globally defined functions. That is the cause. I guess everyone which uses Angular apps on Classic Pages will get this error.
