Let's Encrypt SSL will no longer support Android OS prior 7.1
As of January 11, 2021, we’re planning to make a change to our API so that ACME clients will, by default, serve a certificate chain that leads to ISRG Root X1
However, this does introduce some compatibility woes. Some software that hasn’t been updated since 2016 (approximately when our root was accepted to many root programs) still doesn’t trust our root certificate, ISRG Root X1. Most notably, this includes versions of Android prior to 7.1.1. That means those older versions of Android will no longer trust certificates issued by Let’s Encrypt.
Whether you need to run a banner asking your Android users on older OSes to install Firefox, stop supporting older Android versions, drop back to HTTP for older Android versions, or switch to a CA that is installed on those older versions.
Your thought on this?