Menu link "Inaccessible" for anonymous users if page is archived

This is the expected behavior when something renders an inaccessible link. Are you absolutely sure the site has no menu-related contributed modules, no custom code rendering menu links, and no related patches applied?

You mentioned not knowing how to debug this. Here's how:

1. Setup and start a PHP debugger.
2. Put a breakpoint in Drupal\Core\Menu\InaccessibleMenuLink::getTitle().
3. When execution stops at the breakpoint, observe the call stack.

P.S. Drupal 9 reached end-of-life last year and is no longer supported.

Thanks for your help, @cilefen. There aren't any menu-related contrib modules, but there is a ton of custom code (it's a site I inherited). There is a menu-related custom module, but I'm not sure how it would cause this issue because it's implementing hook menu_edit_form_alter. The only patch being applied is for viewsreference, so that shouldn't be a problem. We have another Drupal 9.5 site and it doesn't have the same issue (the inaccessible links don't appear for anonymous users), but that site is built in a more standard way (less custom code). I've struggled getting xcode working with phpstorm and lando, so I was just hoping someone might have had experience with this problem and what might have fixed it for them in the past. I found this:

// Only render accessible links.
      if ($data->access instanceof AccessResultInterface && !$data->access->isAllowed()) {
        continue;
      }

in /web/core/lib/Drupal/Core/Menu/MenuLinkTree.php (line 245), so it seems like the links shouldn't be displaying.
Thank you for the tip about debugging. I'll try to get xdebug working (fingers crossed!).