How can I get back lost internet access?

I have an Acer A500 tablet running Android 4.0.3. Trying this after not using for some time I find it can’t access most websites, getting "Webpage not available" in Opera Mini browser. I have found an interesting web page (using my desktop) at

Following up a link on this page, it says there has been a workaround by Let’s Encrypt which will last till 2024, and doesn’t need users to make any change. If that’s so, it doesn’t work for me. Can anyone help?