mac showing "not secure" in browser

Hi,

I've been having this problem with Macbook air for the last several months. When I visit various website with, either through Chrome or Safari, it shows the "not secure" message in the browser tab. On some sites, I'm unable to access certain functions and unable to view certain images on the website as a result. The "not secure" message has been showing up on many sites, which leads me to believe it's an issue with mac browser rather than the website itself being not secure.

Can you please assist?

Thank you,

athina