How to resolve The _AppComponent component is not marked as standalone, but Angular expects to have a standalone component here

I was migrating from standalone component to module based where I changed and even tried to remove standalone in the decorator in the appcomponent, and in main.ts file I imported platformdynamic and bootstrapModule to the main module and in module file I declared the appcomponent and bootstrap it still it's generating runtime error 'Internal server error: NG0907: The _AppComponent component is not marked as standalone, but Angular expects to have a standalone component here. Please make sure the _AppComponent component has the standalone: true flag in the decorator.'

Here is the relevant code:

app.module.ts file:

import { NgModule } from "@angular/core";
import { BrowserModule } from "@angular/platform-browser";
import { AppComponent } from "./app.component";
import { HeaderComponent } from "./header/header.component";
import { UserComponent } from "./user/user.component";
import { TasksComponent } from "./tasks/tasks.component";

@NgModule({

declarations: [AppComponent],
bootstrap: [AppComponent],
imports:[BrowserModule, HeaderComponent, UserComponent, TasksComponent]
 })
 export class AppModule{

  }

app.component.ts file:

import { Component } from '@angular/core';
import { DUMMY_USERS } from "./dummy-users";

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrl: './app.component.css'
 
  })
 export class AppComponent {}

main.ts file

import { platformBrowserDynamic } from "@angular/platform-browser-dynamic";

import { AppModule } from "./app/app.module";

platformBrowserDynamic().bootstrapModule(AppModule).catch(err => console.error(err));

the runtime error which I'm getting is:

I think i understood your problem.I guess your project is on angular 19.So by default the components are standalone and u need to refer false to make is not stand alone.

and along with that you must take care of the main.server.ts at the root. it's for ssr but I am sure u never touched it. Here is the problem .Solve it accordingly Goto angular.json file and

    // "server": "src/main.server.ts",
    // "outputMode": "server",
    // "ssr": {
    //   "entry": "src/server.ts"
    // }

comment out this section.

make AppComponent standalone to false.

the rest should be okay.Ur code is prefect. Now restart the app , and it should be okay now.