Media Center doesn't contain an adblocker, so it's strange that MC26 wouldn't have ads but MC28 does. Maybe it's related to the new Edge WebView2 engine being used.
Anyways, since there's no way to add extensions to the embedded web browser, the only way to block YouTube ads unfortunately is with a YouTube Premium subscription which requires one to login with a Google account, assuming Google hasn't blocked that yet in the WebView2 version of Edge.