I am using the HyperDock OSX app. https://apps.apple.com/us/app/hyperdock/id449830122?mt=12
One of the features of this tool is that when you drag any app on the top-header of your screen, it goes full screen. If you drag it to the left, the window will resize to the half of the screen and same for the right.
Few months ago, it was working perfectly with Opera but I realized it does not work anymore while there is no problem for other apps (Word, Safari, Firefox for instance).