Threshold for Lists SharePoint Online & Export Calendar to Outlook
The threshold of the lists (including calendars) is 5000 currently. Once the limit is exceeded, it seems that there's nothing you can do with the list. You can't open / edit / delete any events, can't export the calendar items, can't open with Outlook or Acess, ... Of course that you can't change the threshold either. The threshold should be allowed to change, or there should be a way to export the data. Most businesses will have more than 5000 events in their public calendars. This is very inconvenient for business users.
Another suggest is to add the export SharePoint calendar to Outlook function.
Pam Barber commented
Views can be set up as per https://support.microsoft.com/en-us/office/manage-large-lists-and-libraries-in-sharepoint-b8588dae-9387-48c2-9248-c24122f07c59?ui=en-us&rs=en-us&ad=us
But, it would be nice if Outlook and other apps would honor the default view of the list, to allow for opening with Outlook/access, etc.