If UAC is enabled for the computer and account you are using, then you should not run Opus as admin under UAC. The message in the titlebar is there to remind you that you're running Opus in an unsupported way which will break certain things.
You should not normally need to run Opus as admin, since Opus supports UAC elevation itself, and also has an admin mode that lets you keep a window elevated without multiple UAC prompts.
The warning will go away by itself if you either run Opus normally or disable UAC for the machine or account you are using. More details are in the guide I linked to.