Order Entries Query by a Featured Light Switch

You're looking for the filter filter. Here's how you might do it:

{% set entriesInCat = craft.entries.relatedTo(category).all() %}
{% set featuredEntriesInCat = entriesInCat|filter(entry => entry.yourLightswitchFieldHandle) %}
{% set remainder = entriesInCat|without(featuredEntriesInCat) %}

{% for item in featuredEntriesInCat %}
    <h2>{{ item.title }}</h2>
{% endfor %}

<hr>

{% for item in remainder %}
    <h2>{{ item.title }}</h2>
{% endfor %}

You can add an orderBy clause to the query, and order by the lightswitch field. For example, to fetch all the entries in section things, with the ones with the featured lightswitch turned on first, do this:

  {% set things = craft.entries({
    section: 'things',
    orderBy: 'featured desc'
  }).all %}

To anyone else that needs to something similar:

{% set query = {
  section: 'case_studies',
  limit: entry_limit,
  orderBy: 'featured desc, postDate desc',
}%}

The pagination is wonky without the secondary orderBy parameter. I'm guessing it's because the field for an inactive lightswitch is empty in the DB? I'm speculating, but prior to adding that it would just show the same projects over and over again.

I appreciate all who answered.