Why a Secure Website Can Still Show HTTPS Connection Errors

https://fun-wiki.win/index.php/Why_a_Secure_Website_Can_Still_Show_HTTPS_Connection_Errors

A secure website can still show HTTPS errors when its certificate is expired, issued for a different domain, or signed by an unrecognized authority. Mixed content—like images from unprotected servers—also triggers warnings because parts of the page aren't encrypted. Your browser's outdated root store or incorrect system time can cause false alarms too, making even properly configured sites appear insecure.