Sorry to bring this post back from the dead a 2nd time, but I'm getting some unwanted results from this as well. I'll try my best to summarize:

Normally I use ctrl+scroll to zoom in and out on webpages, but on pages with built-in maps like Roll20 (virtual tabletop), it's not a great idea to use ctrl+scroll to for zooming, because if you accidentally move your mouse over any of the interface elements, then suddenly you're zooming in/out on the whole page. So I've gotten the habit of using alt+scroll for that.

So, I made the switch from Chrome to Opera GX a few months ago, and everything is great except for 2 problems, 1 is "dragging files between monitors opens sidebar items" which is a problem for another day, and the other is this. To this day, every Thursday night when I go to play D&D, I either have to remember to open another browser, or if I'm too lazy to, I have to suffer that menu dropping down every time I zoom in or out. It's not the only issue I have using Opera for Roll20, but the other issues are minor and easy to look past.