When you use a re-webber proxy (a website where you enter a URL and it shows you the content of that url in its own context), using TLS between you and the end-website becomes impossible, even when the proxy would want to provide it.
When you enter
https://google.com in the proxy you linked, you get redirected to
https://www.zend2.com/vip3.php?u=RyhEPtB1SQ6bFRGMjVSDaC2jhw%3D%3D&b=29. Note that the domain you connect to is
https://www.zend2.com. That's the domain you make your TLS handshake with. Anything else would lead to a certificate warning, because your browser expects a valid certificate from
www.zend2.com, not from
google.com. The proxy then does its own TLS handshake with the destination site, requests the content, decrypts it, COULD look at it, re-encrpyts it for you and sends it to you.
To avoid this, do not use a rewebber service. Use a proxy server properly by entering it into the connection settings for your web browser. In that case your web browser is aware that it is using a proxy server and will expect a TLS certificate from the actual destination, not from the proxy. Any eavesdropping or manipulation by the proxy become impossible in that case.