Exclude custom post type archive from the sitemap

We have a CPT called “templates” which have a taxonomy called “categories”.

The template categories are part of the sitemap index:
https://mandoemedia.com/templatecategory-sitemap.xml

We don’t use the template category archive pages on the front-end. The categories are purely for grouping on complex WP pages.

If I visit Search Appearance > Archives, (/wp-admin/admin.php?page=wpseo_titles#top#archives), I see Template Categories are not visible to make them indexable or not.

How do I make Template Categories not indexable, so they’re removed from the sitemap?

Is there a programmatic way to do so in functions.php?

Thanks.

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