What is the underlying version of your Android phone? If it is earlier than Android 7.1.1, then be careful.
The certificate management agency Let’s Encrypt warned that it plans to stop the default cross-signature authentication of the mobile phone system from January 11, 2021, and completely abandon it from September 1, 2021.
This means that a large number of websites that use security certificates will not be accessible on systems earlier than Android 7.1.1.
Although Mozilla and Let’s Encrypt have a cooperation, using the FireFox browser will solve some webpage opening problems, but not all of them, and how long it will last is unknown.
According to data, there are currently about 33.8% of Android users running on 7.1 and older systems, which is not small.
If your phone cannot be upgraded to Android 7.1.1 and above, you may have to consider replacing it with a new phone for safety and user experience considerations.