Right-click on Opera's shortcut (or right-click on the Opera taskbar button and right-click on "Opera Browser") and goto "properties". Switch to the "shortcut" tab and edit the target field value. Add a space and then --disable-gpu. If Opera is already open when you do this, close it down and open it back up with the shortcut.

Opera should then load where you can goto the URL opera://settings/system and disable hardware acceleration. Then you can remove the --disable-gpu form the shortcut's properties if you want.

Not sure why it's happening. Opera doesn't lke something about your GPU and or GPU driver.