I also have this issue. If you exit full screen and re-enter it, it goes away. The second you tab away or switch to another screen in mission control it comes right back. Very annoying bug.
Posts made by sugarbun
RE: MacOS menu bar vertical space preserved in fullscreen modeOpera for Mac
RE: Video Playback on Mojave not working everywhereOpera for Mac
@wolkix3 Also have this issue since updating to Mojave.