For anything that is not about one event, use an announcement
The notify checkbox only reaches the people signed up for that one event. To write to the whole group, build a CMS page and send it as an announcement - Announcements under Content.
The list of who is coming is on the event page itself, not in the admin area. What the admin side adds is the count in the event list and the ability to email everyone who signed up when something changes.
The Events list under Content has an Rsvp column, so you can see how full each event is without opening it. The event's own public page has the attendee list in full: one tile per person, with a guest count on the tiles of people bringing someone. The admin dashboard also collects upcoming events with low RSVP, which is the earliest warning that something needs a nudge.
Open the event for editing
From the Events list under Content. The notice at the top tells you how many people have already committed.
Make the change worth telling them about
A new time, a new venue, something to bring. Put it in the description if it should persist on the page.
Tick Notify and save
The mail goes out to the RSVP list on save. Members who turned off "Updates to events I plan to attend" will not get it.