Joining an online Webinar meeting will attempt to get the user to perform a software install which is not possible on CONNECT.
But there is a web version, although its not obvious and not suggested to the user at the point of entry.
Try Join the Webinar | GoTo Webinar (web App) for Chrome as Chrome extensions are "normally" Edge compatible?
They'll also need to ensure that they grant the browser access to your Microphone and possibly your camera too, see below for how you would achieve this.