iMac 24”M1 2024 Sequoia 15.6.1. Safari opening page shows Connection not secure. How to fix it?all

Perhaps that page is not using TLS, in which case the connection is not secure.

Try a different website, such as www.apple.com. Same problem?

I have noticed the same problem. Since upgrading to Sequoia, random sites are displaying the "Connection not secure" message, including a site I manage, that I know is fully secure, uses HTTPS, non-expired certificate, etc. Often, reloading the page fixes the error, but sometimes, the site remains inaccessible. I am seeing this with large, mass-market sites like cnn.com, in addition to smaller corporate sites. It has become random, where I will access a site in the morning, and in the afternoon, it is blocked. I know multiple workarounds for this issue, but it's still annoying.