Communication Site Events - no support for recurring events?

The Events web part, regardless of the site it's used in, doesn't handle recurrence in either its UI (as you showed in your screenshot) or its end-user display. I don't think Microsoft believes this is a bug, rather functionality that just isn't supported yet. What Events doesn't really tell you is it's using a SharePoint calendar to store events (go look around your site for a calendar and you'll find the events are the same); while the Calendar does support recurrence, it's still a "classic" application with no Modern version. I suspect that when Microsoft gets around to Modern-izing the Calendar app, it'll sort out the lack of support for Recurrence in Events. I've not heard a timeline for this.