How to resolve The _AppComponent component is not marked as standalone, but Angular expects to...

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));

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