MacBook Pro
I can open website
it says Your connection to this site is Not secure
iPhone 7 Plus, iOS 13
If you see a "Not Secure" warning while browsing the web
That Support document discusses Safari on iOS but the principles are the same. The most important information it contains is a warning not to provide sensitive information (names, passwords, credit card information, etc) to that website, since that information can be intercepted by potentially malicious actors.