You installed Omni Sidekick, but no icon appears in the toolbar, so you cannot tell whether it is running.
New extensions are not pinned by default. Chrome puts them behind the puzzle piece menu until you pin them, and a disabled extension shows no icon at all.
Click the puzzle piece icon in the toolbar, look for Omni Sidekick, and click the pin next to it. If it is not listed, open chrome://extensions and check that the extension is present and its toggle is on. Once enabled and pinned, the icon gives you quick access to captures, the side panel, and settings.