Here is how to apply prismjs to your code in Angular.
By following this method, you will be able to apply prismjs to HTML stored in a database and display it on an Angular page.

angular-prismjs-example

Edit on StackBlitz ⚡️

The steps are as follows:

1. Install module

npm install prismjs

2. Add services

src/services/

• prism.service.ts
• html-utils.ts
• safe-html.pipe.ts
• shared.module.ts

prism.service.ts

import { isPlatformBrowser } from '@angular/common';
import { Inject, Injectable, PLATFORM_ID } from '@angular/core';

// importing prismjs order is important!
import 'prismjs';

import 'prismjs/plugins/toolbar/prism-toolbar';

import 'prismjs/plugins/copy-to-clipboard/prism-copy-to-clipboard';
import 'prismjs/plugins/line-numbers/prism-line-numbers';
import 'prismjs/plugins/show-language/prism-show-language';

import 'prismjs/components/prism-csharp';
import 'prismjs/components/prism-css';
import 'prismjs/components/prism-java';
import 'prismjs/components/prism-javascript';
import 'prismjs/components/prism-json';
import 'prismjs/components/prism-markup';
import 'prismjs/components/prism-python';
import 'prismjs/components/prism-sass';
import 'prismjs/components/prism-scss';
import 'prismjs/components/prism-sql';
import 'prismjs/components/prism-typescript';
import 'prismjs/components/prism-visual-basic';
import 'prismjs/components/prism-xml-doc';

// eslint-disable-next-line @typescript-eslint/no-explicit-any
declare const Prism: any;

@Injectable({
  providedIn: 'root', // can inject anywahere
})
export class PrismService {
  constructor(@Inject(PLATFORM_ID) private platformId: object) {}

  highlightAll() {
    if (isPlatformBrowser(this.platformId)) {
      Prism.highlightAll();
    }
  }

  highlightHtml(html: string): string {
    const div = document.createElement('div');
    div.innerHTML = html;
    const codeElements = div.querySelectorAll('code');
    codeElements.forEach((el) => {
      const lang =
        el.getAttribute('class')?.replace('language-', '') || 'javascript';
      el.innerHTML = Prism.highlight(
        el.textContent || '',
        Prism.languages[lang],
        lang
      );
    });
    return div.innerHTML;
  }
}

html-utils.ts

export function addClassToHtml(
  html: string,
  className: string,
  tagName: string
): string {
  const parser = new DOMParser();
  const doc = parser.parseFromString(html, 'text/html');
  const elements = doc.querySelectorAll(tagName);
  elements.forEach((el) => {
    el.classList.add(className);
  });
  return doc.documentElement.innerHTML;
}

safe-html.pipe.ts

import { Pipe, PipeTransform } from '@angular/core';
import { DomSanitizer, SafeHtml } from '@angular/platform-browser';

/** usage
 * [innerHTML]="value | safeHtml"
 */
@Pipe({ name: 'safeHtml' })
export class SafeHtmlPipe implements PipeTransform {
  constructor(private sanitizer: DomSanitizer) {}

  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  transform(html: any): SafeHtml {
    const result = this.sanitizer.bypassSecurityTrustHtml(html);
    return result;
  }
}

shared.module.ts

import { NgModule } from '@angular/core';
import { SafeHtmlPipe } from './safe-html.pipe';

@NgModule({
  declarations: [SafeHtmlPipe],
  exports: [SafeHtmlPipe],
})
export class SharedModule {}

3. Add prismjs style to global style sheet

global_styles.css

/* Add application styles & imports to this file! */

/* Prismjs theme */
@import "prismjs/themes/prism-okaidia.css";
@import "prismjs/plugins/toolbar/prism-toolbar.css";
@import "prismjs/plugins/line-numbers/prism-line-numbers.css";
/* Available themes */
/*
@import "prismjs/themes/prism.css";
@import "prismjs/themes/prism-coy.css";
@import "prismjs/themes/prism-dark.css";
@import "prismjs/themes/prism-funky.css";
@import "prismjs/themes/prism-solarizedlight.css";
@import "prismjs/themes/prism-tomorrow.css";
@import "prismjs/themes/prism-twilight.css";
*/

4. Apply prismjs to html

main.ts

@Component({
  selector: 'my-app',
  standalone: true,
  imports: [CommonModule, SharedModule],
  templateUrl: './main.html',
  styleUrls: ['./main.scss']
})
export class App implements OnInit,AfterViewChecked {
  name = 'Angular';

  highlighted = false;

  code = `
  <p>Here's how you can customize the appearance of an Angular Material toggle button. Although the method is unique, I'll explain it in this article.</p>\n<h2>1. How to use Angular Material button-toggle</h2>\n<h3>Install Angular Material</h3>\n<pre><code class=\"language-bash\">ng add @angular/material\n</code></pre>\n<h3>Import Angular Material button-toggle to Module file</h3>\n<pre><code class=\"language-ts\">import {MatButtonToggleModule} from '@angular/material/button-toggle'\n</code></pre>\n<h3>Html</h3>\n<pre><code class=\"language-html\">&lt;mat-button-toggle [aria-label]=&quot;alertsEnabled ? 'Disable alerts' : 'Enable alerts'&quot;&gt;\n  &lt;mat-icon&gt;notifications&lt;/mat-icon&gt;\n&lt;/mat-button-toggle&gt;\n</code></pre>\n<p>For more details, refer to the official documentation:<br>\n<a href=\"https://material.angular.io/components/button-toggle\">Angular Material Official Documentation</a></p>
`;

  constructor(private readonly prismService: PrismService) {}

  ngOnInit(){
      this.code = HtmlUtils.addClassToHtml(this.code, 'line-numbers', 'pre');
  }

  ngAfterViewChecked() {
    if (!this.highlighted && this.code) {
      this.prismService.highlightAll();
      this.highlighted = true;
    }
  }
}

main.html

<h1>Hello from {{name}}!</h1>
<a target="_blank" href="https://angular.io/start">
  Learn more about Angular sample
</a>

<div [innerHtml]="code | safeHtml"></div>