While answering to https://github.com/twbs/bootstrap/issues/36684, I may have spotted an issue regarding the definition of --#{$prefix}nav-link-font-size and --#{$prefix}nav-link-font-weight in .navbar-nav.
Without this fix, locally, if you change this in _variables.css:
$nav-link-font-size: 30px !default;
$nav-link-font-weight: 700 !default;The change is only observable in pages like /docs/5.2/components/navs-tabs/ that use .nav and .nav-links inside.
The change is not observable in the main header of the docs for example that use .navbar-nav and .nav-linkss inside.
With this fix we can see the big bold font everywhere where we have .nav|.navbar-nav and .nav-links inside.