You should be able to go into Settings -> Install Apps in Windows and remove the Live wallpaper helper.

Or, you should be able to goto the URL opera://settings/live_wallpapers in Opera and choose "remove".

Or, you should be able to delete the "Opera GX Live Wallpaper" folder "C:\Users\yourusername\AppData\Local\Programs". Then, you can open up regedit and delete the install entry. It should be under "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Uninstall". In my case the key is "{47D37748-C896-49C1-B20F-AB60EBC4FEB1}_is1".

You can also remove the live wallpaper entry from "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run" so no command tries to run when Windows starts.