In Neno Breadcrumbs are built into the theme. To activate Breadcrumbs, navigate to General -> Breadcrumbs in the WordPress Customizer.
If you are using Yoast SEO, RankMath or SEOPress with Neno, their breadcrumbs will be shown instead of the built-in breadcrumbs of the theme. Some SEO plugins require you to activate Breadcrumbs for them to appear on your website. In the case of Yoast SEO for instance, make sure to activate breadcrumbs under SEO -> Search Appearance -> Breadcrumbs.