Calendars where people already saved the event only update if those people subscribed to the whole collection. The location short link is the exception: it always points to the current meeting link.
Subscribed to the collection: Yes. New and changed events of the collection reach their calendar automatically.
Added this one event to their calendar: No. Their calendar keeps the copy they saved.
Has the link and opens it again: Yes. The event page always shows the current details.
The edit form shows this as a reminder: "Updates will not automatically appear for events already added to a calendar unless the user is subscribed to the full collection. However, the location URL will always redirect to the most current link."
Keep attendees up to date
Online events: leave Shorten URL on. If the meeting link changes, the short link in everyone's calendar forwards to the new one. See Add an online meeting link.
Events that change often: share the collection page instead of a single event, so visitors can subscribe and receive updates. See Create and manage collections.
RSVP events: download the registrations and email the attendees about the change. See View, edit and export registrations.
A new time or date: tell people to add the event again from its page. Their old calendar entry does not move by itself.