I don't think that's correct per https://letsencrypt.org/certificates/ https://letsencrypt.org/certificates/ Our intermediate is signed by ISRG Root X1. Howeve

I don't think that's correct per https://letsencrypt.org/certificates/ https://letsencrypt.org/certificates/ Our intermediate is signed by ISRG Root X1. However, since we are a very new certificate authority, ISRG Root X1 is not yet trusted in most browsers. In order to be broadly trusted right away, our intermediate is also cross-signed by another certificate authority, IdenTrust, whose root is already trusted in all major browsers. Specifically, IdenTrust has cross-signed our intermediate using their DST Root CA X3.