It does not show up

You provided https://www.screenprintingnow.com/ as the URL you are having an issue with. Your home page will not have Schema Breadcrumb markup as it is not part of a hierarchy – there’s no parent relationship to describe. Using https://www.screenprintingnow.com/equipment/screen-printing-flash-cure-units/ as an example (which does have parents), I can see that the Schema Breadcrumb markup is being added correctly:

        {
            "@id": "/equipment/screen-printing-flash-cure-units/#sso/breadcrumb.list/equipment",
            "@context": "https://schema.org",
            "@type": "BreadcrumbList",
            "url": "https://www.screenprintingnow.com/equipment/screen-printing-flash-cure-units/",
            "itemListElement": [
                {
                    "@context": "https://schema.org",
                    "@type": "ListItem",
                    "position": 1,
                    "name": "Home",
                    "item": "https://www.screenprintingnow.com/"
                },
                {
                    "@context": "https://schema.org",
                    "@type": "ListItem",
                    "position": 2,
                    "name": "Screen Printing Equipment",
                    "item": "https://www.screenprintingnow.com/equipment/"
                },
                {
                    "@context": "https://schema.org",
                    "@type": "ListItem",
                    "position": 3,
                    "name": "Screen Printing Flash Cure Units",
                    "item": "https://www.screenprintingnow.com/equipment/screen-printing-flash-cure-units/"
                }
            ]
        }

js.

Oh ok, means, it is only there for google and not the user!?
Regards

https://wpsso.com/docs/plugins/wpsso-breadcrumbs/faqs/how-can-i-add-wpsso-breadcrumbs-to-my-theme/

js.