Older Android phones will no longer be able to see enough secure websites as of September 2021.
You may need to upgrade Android phone and not upgrade to buy a new one if you want to visit secure pages that use https. According to Android Police, the Let's Encrypt certification company he warned that phones running Android versions before Nougat 7.1.1 will not trust root certificates starting in 2021.
The result will be that they will not be able to view enough secure web pages. The organization will stop on January 11, 2021 the default cross-signature for the certificate that allows this functionality and will withdraw its partnership on September 1 of the same year.
A workaround is available to install Firefox (Mozilla is a Let's Encrypt partner) using its own store certificates, but this will not help the rest of the broswers or the functionality beyond the programs browsing.
It is a habit for developers to drop support for older operating systems. Let's Encrypt noted that about 33,8 percent of Android users on Google Play has a version older than 7.1 and some hardware vendors cut their support relatively early.
This means that you may have bought a low-cost phone in 2016 or even 2017 that could suddenly lose access to some sites, and without having a solution.