Https and SSL

I have encrypted my domain name on SiteGround, But WordPress still reminds me that I am not using a secure connection.
After SiteGround’s customer service check, there is no problem with domain name encryption. They let me clear the cache. I used CCleaner to clear all the caches on the browser. After logging in to WordPress again, it still shows that I am not using a secure connection. Anyone has experienced this problem? How to solve it? How to add pictures here?