Hi,
As I can read here in french :
https://web.developpez.com/actu/310287/Sur-les-anciennes-versions-d-Android-de-nombreux-sites-securises-par-Let-s-Encrypt-pourraient-cesser-de-fonctionner-en-2021-un-tiers-des-appareils-Android-sont-concernes/
Let’s Encrypt will issue certificates that won’t work for old Android devices next year.
A way to continue accessing those websites will be to use Firefox Mobile or IceCat Mobile:
Happy browsing !