Modal not working with Bootstrap 3 theme

Problem/Motivation

Based on issue #3419110 → , the modal is no longer displayed, and a JavaScript error has reoccurred.

dialog.js?v=10.2.6:29 Uncaught ReferenceError: bootstrap is not defined
    at Drupal.behaviors.externalLinkPopup.openDialog (dialog.js?v=10.2.6:29:21)
    at HTMLAnchorElement.<anonymous> (dialog.js?v=10.2.6:69:23)
    at HTMLBodyElement.dispatch (jquery.min.js?v=3.7.1:2:40035)
    at v.handle (jquery.min.js?v=3.7.1:2:38006)

Steps to reproduce

1. Install Drupal 9/10.
2. Install and set Bootstrap 3 → as site's default theme.
3. Install Bootstrap External Link Pop-up → module and create a test content.(Add random external URL(s) in the content).
4. Once node is saved, access the node and click on the added external URL(s).

It doesn't open the modal.

Proposed resolution

Make it compatible for both versions(Bootstrap 3.x, Bootstrap 4.x and Bootstrap 5.x).

Remaining tasks

User interface changes

API changes

Data model changes