Info-Mac

I'm using Safari 13.1.1 on my MacBookPro running OSX Mohave 10.14.6.

I have blocked popup windows on all sites in the Safari Preferences dialog: Websites > Popup Windows.

But still when I go to various sites a kind 'preview' of the site appears.
I need to choose Escape to have it go away. This is quite annoying.
It just happened on this site: [link removed]

Any clues for me?
Thank you very much!

If you're experiencing unusual popups I would suggest first scanning your Mac for any malware or adware using Malwarebytes

What Turboladdade said, but also report it to the webmaster if that’s the only site that gives you that pop-up.