Older phones with Android It seems that from September 2021 they will not be able to see enough secure websites.
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 cannot view enough secure websites. The organization will stop on January 11, 2021 the default cross-signature for the certificate which enables this functionality and will withdraw its partnership on September 1st of that year.
A workaround is available to install Firefox (Mozilla is a Let's Encrypt partner) using its own certificate store, but this won't help other browsers or functionality beyond programs browsing.
It is customary for developers to leave την υποστήριξη παλαιότερων λειτουργικών συστημάτων. Το Let's Encrypt σημείωσε ότι περίπου το 33,8 τοις εκατό των χρηστών Android στο Google Play διαθέτουν μια έκδοση παλαιότερη από την 7.1 και ορισμένοι προμηθευτές υλικού έκοψαν την υποστήριξη τους σχετικά νωρίς.
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.
