If you don't care about any of your data and settings etc., you can rename the "Opera GX Stable" folder in both "C:\Users\yourusername\AppData\Roaming\Opera Software" and "C:\Users\yourusername\AppData\Local\Opera Software" to "Opera GX Stable old" to start over completely fresh. Uninstalling and reinstalling doesn't do that unless you tell the uninstaller to delete your data when asked.