I think this might be a bug report, but I'm not sure, so I'm posting it as a questions in case I'm overlooking anything.
Steps to reproduce:
1. Create a new Angular 11 project with `ng new daypilot-test` and accept all defaults
2. Add DayPilot Pro 2021.2.4931 to `package.json` and run `npm install`
3. Add DayPilotModule to the imports in `app.module.ts`
3. Run `ng build --prod`
Build fails with message:
Error: node_modules/daypilot-pro-angular/daypilot-angular.d.ts:121:22 - error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class.
This likely means that the library (daypilot-pro-angular) which declares DayPilotModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.
4. Edit `angular.json` and set `aot` and `buildOptimizer` to `false` in the `production` configuration.
5. Run `ng build --prod`
6. It builds successfully, but is not optimized.
This issue looks similar to an old post: https://forums.daypilot.org/question/4964/ivy-schedulermodule-angular-8
In that post it was mentioned that since v2020.1.4238, Ivy + AOT should be supported.
Is there anything I am overlooking? Also, this seems to work just fine with Angular 9 and 10, but not 11.