From October 2021 onwards, only those platforms that trust ISRG Root X1 will validate Let’s Encrypt certificates ( with the exception of Android). Prior to September 2021, some platforms could validate our certificates even though they don’t include ISRG Root X1, because they trusted IdenTrust’s “DST Root CA X3” certificate. The main determining factor for whether a platform can validate Let’s Encrypt certificates is whether that platform trusts ISRG’s “ISRG Root X1” certificate.
