2021, many sites will stop working on Android 7.1 and older OS..

[sanjay kumar]

Let's Encrypt's initial partnership with IdenTrust expires on September 1, 2021, and the group has no plans to enter into another cross-signature agreement. This means that all browsers and operating systems without the Let's Encrypt root certificate will no longer work with sites and services that use group certificates. The announcement states that devices running Android 7.1 or earlier are included in the vulnerable group:

“However, this does cause certain compatibility issues. Some software that hasn't been updated since 2016 still doesn't trust our ISRG Root X1. First of all, this includes Android versions up to 7.1.1. This means that older versions of Android will no longer trust certificates issued by Let's Encrypt. "

Although the agreement will not expire until September of next year, Let's Encrypt will end cross-signature by default starting January 11, 2021. Sites and services will continue to be able to create cross-signed certificates, but only until September.

The only workaround for legacy Android devices is to install the mobile version of the Firefox web browser, which uses its own certificate store that includes the root ISRG. However, this will not eliminate problems when applications and other functions work outside of this browser...