This test web site, revoked.x1.test-certs-site.certcat.dev, is intended for testing compatibility with Let's Encrypt certificates.
It is using a certificate issued by ISRG Root X1 which is revoked.
Find out more about Let's Encrypt at our homepage, letsencrypt.org.
Other test web sites and information about our certificate hierarchies is available on our Chains of Trust documentation page.