@burnout426 there is a flag called #gemini-in-sidebar that you can enable. That way you don't need to add a custom site panel, it'll just show as an option in the sidebar settings.

Type into the address bar opera://flags/#gemini-in-sidebar, and change the setting from "default" to "enabled". Restart Opera. Navigate to the sidebar settings, and Gemini should now show as an option in the AI Services tab, and the icon will appear next to your other selected AI services and chats.