In my case it was an issue with a second screen again. I used to run Opera on my "left" screen but after changing it to my "right" screen in the windows options menu for display settings it wouldn´t show up. I changed it back to "left" screen, dragged Opera (which was working again) to my middle screen and undid my changes so that the second screen is back on the "right". Thats how I solved it. So if you are using a second screen, make sure, Opera isnt closed on the wrong one before changing screen orientation or the side of it. Leave Opera always on your main screen so itll show up, even when a second monitor is missing.