Hi,

Try the below.

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
    <template id="categ_breadcumb" inherit_id="website_sale.product">
       <xpath expr="//li[hasclass('active')]" position="before">
        <li t-if="len(product.public_categ_ids)==1" class="breadcrumb-item">
            <a t-att-href="keep('/shop/category/%s' % slug(product.public_categ_ids))">
                <span t-field="product.public_categ_ids.name"/>
            </a>
        </li>
       </xpath>
    </template>
</odoo>

Regards