Your screenshot doesn’t include the top bar of the Extension Manager which has a drop down list that controls what you’re looking at: Installed Extensions, Core Extensions, etc.
I assume you’re looking at Installed Extensions and you have subwikis, in which case the list includes extensions installed in the subwikis. From the main wiki you can manage the extensions that are installed anywhere (main wiki, subwiki, on farm). If you click on “Show details” you should be able to see in which wiki each listed extension is installed.
Moreover, you should be aware that the action buttons (like Downgrade) depend on the version being listed and on the version currently installed. If an older version (that the one currently installed) is listed then the Downgrade button is displayed. If a newer version than the one currently installed is listed then the Upgrade button is shown. If not version is installed then the Install button is shown (for the listed version).
In any case, you probably just need to upgrade your subwikis.