Amazing, it is now possible to have a website create a popup window in Opera that you can't move and can't close... Unless you are fortunate enough to know about Alt-Drag to move or Alt-F4 to close... Oh, but wait, that doesn't work on a touch-screen does it?!
https://javascript.info/popup-windows#example-a-minimalistic-window
Like others on this thread, I too am now looking to an alternative unless it looks like this "feature" will be fixed. Vivaldi's looking nice so far.
Edit: Browsing around, found this page:
https://www.htmlgoodies.com/beyond/javascript/article.php/3471181/New-Window-No-Title-Bar.htm
Smiled at the comment from KS at the bottom: That only works in older browsers. Modern browsers won’t let you remove the title bar because then there’s no way to close the window.
Seems that is not so true anymore 😉