Show only subcategories 2.3.0.2

In the category module / tree, I'm looking for a way to show only subcategories when in a main category.

We have a site with hundreds of categories and subcategories. So, when showing the category module on the side, our page is huge.

I've searched the web and found answers for previous versions of OpenCart up to 2.2, but none for 2.3.0.2.

Well, then better link to that information, then, one
could possibly find out, what small differences keep your
version from acting the same ...
Ernie

Thanks Ernie for the reply... here's the link for the one I found - https://webocreation.com/blog/show-only ... ree-module