You have posted this question in the macOS High Sierra Community. Are you running that particular macOS?
If so, know that you are running an obsolete version of macOS which includes an outdated version of Safari.
Internet security features continue to evolve and older versions of Safari cannot negotiate secure connections with newer sites. If you are having trouble connecting to websites with your older version of Safari, try it with a newer third party browser that is still being updated to meet current internet security protocols.
I suggest you take a look at Firefox browser or Brave browser.