So, this is about popups inside of browser windows, is it? And not about popups in Windows/Mac/Linux desktops? Because I couldn't start making up my mind until close to the end of the article.

FWIW, I do make some use of modals in Linux on the Web (source code, admittedly somewhat sloppy: https://github.com/linuxontheweb/LOTW/blob/main/root/code/mo...). In fact, I just tried to make a post about a new app I'm working on (that happens to use them) called "HackerNotify": https://news.ycombinator.com/item?id=32358782