La preview ne s'actualise pas | Twurple API

API
14

new Date() or it’s friend new Date().getTime()

Should return the current date/time always.

So your code should have something like

stream.thumbnailUrl = stream.thumbnailUrl + '?cachebuster=' + new Date();
            const preview = await Manager.twitch.postImage(
                stream.thumbnailUrl
                    .replace("{width}", "1280")
                    .replace("{height}", "720")
            );

So the output of new date() not the literal new Date