I have the same issue with this new install of opera. I can't even log into Last Pass as the extension instructions recommend as there is no icon in the toolbar to click on. The extension options also don't have the Show/Hide icon option like some other extensions do so I have no way to interact with the extension
Opera has a new feature where you can hide extensions from the toolbar. In order to make extensions appear on the toolbar click on the cube icon to the left of the download icon. From there you should be able to see a list of extensions. Click the pin next to the extensions name to pin it to your toolbar.