Ok so i wrote an How-To to downgrade and disable update. But it seems that doesn't get approved. Anyway: disabling the updater doesn't actually disable the updater after two restarts of the browser it still just updates without asking Im offically switching what is the point of and executable flag if it doesn't work!

Can confirm @noavalon 's 'test' to all who want to keep using a fast browser. Do the following:

1. Open this page: http://get.opera.com/ftp/pub/opera/desktop/
2. Scroll all the way down and click on '69.0.3686.95/' (newest one without bug) then on 'win/'
3. Then select corresponding to your machine structure the 'Opera_69.0.3686.95_Setup.exe' (32-Bit) or 'Opera_69.0.3686.95_Setup_x64.exe' (64-Bit) and download it by clicking on it!
4. After the download run the installer and 'IMMEDIATELY' close the opened browser window because it will try to update it again.
5. To prevent the auto updates you have to add '--disable-update' behind the executable target!
   Like this:
   
   Be Aware: This has to be behind every link you open Opera with. otherwise it will just auto-update it!
   Sadly: there is no permanent option to avoid updates just this janky way of tempering with the executable links!