safari can't establish a secure connection to website

So, I was using safari to log-in to Ymail.com. But, the browser couldn't load and says safari can't establish a secure connection to website. I tried using Chrome. It's the same. There are also other sites that the browser can't go.

So I tried using opera and with VPN. I was able to log in to ymail.

Then I went back to logging in to my gmail account - suddenly, I got the same issue - safari can't establish a secure connection to website. Prior to logging to going to Ymail, I have no problem logging in to gmail. I also have no problem logging in to google drive.

I tried asking if the my internet service provider is blocking the sites. But they said they're not doing that.

Does safari or macbook automaticallly stop all these websites from being accessed?

I have tried everything, change the DNS, remove cache, reset network settings, change IPv6 to manual. Still no luck! I'm freaking out because google is the one we only use for work!

Can anyone help?

I'm running the latest version of MacOS Catalina and Version 14.0 (15610.1.28.1.9, 15610) of Safari.