You can close the registrations for your event and still keep your event published so that your invitees can access the event website and view all the event-relevant information.
Here are the steps for closing your event RSVPs:
Open your event dashboard and click on the "Registrations/RSVP Open" option to trigger the dropdown menu:
Choose the "Closed" option and customize the message that will be displayed on your event form side of the event preview:
This is the final result of what your event form page will look like for your invitees: