Looks like Angular Ivy not ready yet. I'm trying to build my project using ivy which is the main idea for Angular 9. Many of libraries are not compatible with this feature, one of these library is @angular/flex-layout. Material and service-worker have the same problem as well.
After using ng build --prod --aot -c=production script to build my project I got:
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node_modules/@angular/flex-layout/core/typings/media-trigger/media-trigger.d.ts:71:18 - error TS2314: Generic type 'ɵɵFactoryDef' requires 2 type argument(s).
71 static ɵfac: ɵngcc0.ɵɵFactoryDef<MediaTrigger>;
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node_modules/@angular/flex-layout/extended/typings/show-hide/show-hide.d.ts:18:18 - error TS2314: Generic type 'ɵɵFactoryDef' requires 2 type argument(s).
18 static ɵfac: ɵngcc0.ɵɵFactoryDef<ShowHideStyleBuilder>;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
node_modules/@angular/flex-layout/extended/typings/show-hide/show-hide.d.ts:49:18 - error TS2314: Generic type 'ɵɵFactoryDef' requires 2 type argument(s).
49 static ɵfac: ɵngcc0.ɵɵFactoryDef<ShowHideDirective>;
The error longer than what I wrote above, I took my time to have a good search for this issue, nothing on the table but disabling ivy which is not a good option.