Question Editor Buttons When Clicked Not Displaying Modal

In the BBCode Editor, when I click on the editor buttons such as the link button, that will open a modal, the modal will not open. Therefore, nothing happens and there is no error message in browser's web developer console. Is there any setting or plugin that I need to enable?

I tried adding the modal CSS - did not do anything. In the console, I am not getting the jquery error where there could be more than one jquery.

I switched to the WYSIWYG editor, the link button works. To change the editor, I went to the Kunena component->Template->Crypsis->BBCode tab->first field, editor - switch from BBCode to WYSIWYG. It says that if you switch to WYSIWYG, the BBCode plugins won't work. I don't use most integration plugins. Besides that, I am not sure what I would lose by using the WYSIWYG editor.

Here is my environment:
Joomla 3.9.3, PHP 7.3.2, Kunena 5.1.10.1, Crypsis template, Joomla template- JoomShaper Empire 1.7

My computer is on my company's intranet therefore I cannot provide you a URL for testing.

It's hard if you can not see the page. It can have many causes, e.g. a script conflict with your Joomla template or an extensions plugin. Also a css conflict is possible.
Try to test it with the Joomla default template Protostar.
Test also whether the modal in principle works with Kunena. Go in the backend to Kunena -> Templates -> Crypsis and choose the setting Type Quickreply = Modal, then try in the frontend an answer with the Quick Reply button. It should open a Modal.

I don't use most integration plugins. Besides that, I am not sure what I would lose by using the WYSIWYG editor.

I think, they are options which in an intranet are not important. Examples: Ebay, Tweet, Instagram and so on... but you can to enter this codes also manually, if you click in the Wysywig editor on the symbol BBCodes.
Smileys work if you enter the combinations of charakters manually.
Only polls are not possible without BBCode etitor.