Tabbed display of posts by category (2ndary menu workaround)

I'm working on a site that includes a fairly large set of leadership profiles.

I'm using posts and categories to separate employees into groups by their location.

I originally intended to set up a tabbed structure for the page, with each tab loading a different post category, but I can't find a plug-in that will do this.

For that matter, I had planned to use Elementor Pro for the site, but its tab structures can't display posts by categories.

So as a not-what-I-wanted-but-what-else-can-I-do solution, I added a secondary menu just to the page on which the posts appear. Of course, to do that, I had to use a regular page, given that you can't add a secondary menu to the posts page.

I don't like the way it looks yet, because the menu is miles away from the left edge of the window, but I haven't finished tinkering with sidebar settings yet. For that matter, none of the personnel head shots are there; just the bio text.

The biggest problem, however, is that none of the sets of profiles will load unless and until the visitor actually clicks on one of the "tabs" (menu levels). So what you get is a blank page with a nav system.

Any way to get the page to load _with the first set of profiles already visible?

(Please don't share the URL with anyone; it's entirely private at this point.)

WP 5.4.2
GP 2.4.2 (with a child theme)
GPP 1.10.0