I've already changed it. If I load "www.google.es" the page shows me well, but if I do it with "https://meet.jit.si/xxxx" the black background remains and only the zoom buttons are visible.I wanted to add a jit.si room to the app, but this work is beyond me.
A webview is only a mini version of a full blown browser. Even in a real browser, this site contains all kind of errors so I doubt a webview will be able to handle it.