Why this error ?? : This type of errors will come in Angular Components. Suppose if you using the angular component which is not declared in that module.
Explanation : The above picture shows the following console error Component ContactComponent is not part of any NgModule or the module has not been imported into your module.
Here ContactComponent is not declared in appModule.ts (please check the following picture ContactComponent is not declared)
Solution : Declare the ContactComponent in app.module declarations array. please check the below image.