Progress indication throbber for remote events operations on high-latency / slow servers
I use GNOME Calendar mostly to interface with nextcloud servers and those are slow as dogs. Creating or modifying events often take multiple seconds. For example, one of the corporate nextcloud instances I interact with is on the other side of the atlantic, and it takes eleven seconds between the moment I "create" the event (in month view) and the moment it appears in the cell in GNOME Calendar.
Short of making everything instantaneous (unlikely), I think it would be good for GNOME Calendar to take a "defensive" approach to the backends and have a quickie timer that checks if it's been more than 150-200 miliseconds since the request for creating/modifying the event has been sent, and if so, display a temporary GtkRevealer (or floating GtkOverlay like what happens when you delete an event in version 43.x and newer) to show a spinner that says "Creating event..." until the event creation acknowledgement has been received from the backend and the UI reflects the change.