Older versions of iPhone OS aren't new enough to have modern certificate authorities trusted, meaning only sites using older certificate authorities are able to have a secure connection.
Certificates:
👉ISRG Root X1 CA (+Let's Encrypt)👈
👉ISRG Root X2 CA👈
👉All Certificates👈
Click to add Directly to Cydia
git clone --filter=blob:none https://github.com/LukeZGD/Legacy-iOS-Kit
https://github.com/LukeZGD/Legacy-iOS-Kit/releases/download/latest/Legacy-iOS-Kit_v26.01.21.zip